Illumination frame of reference in the object-reviewing paradigm: A case of luminance and lightness.

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J Exp Psychol Hum Percept Perform. Author manuscript; available in PMC 2016 December 01. Published in final edited form as: J Exp Psychol Hum Percept Perform. 2015 December ; 41(6): 1709–1717. doi:10.1037/xhp0000123.

Illumination Frame of Reference in the Object-Reviewing Paradigm: A Case of Luminance and Lightness Anja Fiedler and Cathleen M. Moore Department of Psychology, The University of Iowa, USA

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The present study combines the object-reviewing paradigm (Kahneman, Treisman, & Gibbs, 1990) with the checkershadow illusion (Adelson, 1995) in order to contrast the effects of objects’ luminance versus lightness on the object-specific preview benefit. To this end, we manipulated objects’ luminance and the amount of illumination given by an informative background scene in four experiments. In line with previous studies (Moore, Stephens, & Hein, 2010), there was no object-specific preview benefit when objects were presented on a uniformly colored background and luminance switched between objects. In contrast, when objects were presented on the checkershadow illusion background which provided an explanation for the luminance switch, a reliable object-specific preview benefit was observed. This suggests that object correspondence as measured by the object-reviewing paradigm can be influenced by scene-induced, perceived lightness of objects’ surfaces. We replicated this finding and moreover showed that the scene context only influences the object-specific preview benefit if the objects are perceived as part of the background scene.

Keywords illumination frame of reference; luminance; lightness; object updating; object-reviewing paradigm

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Visual objects are usually embedded in dynamic and meaningful scenes that influence how we perceive the objects’ surface features. One example of this is the perception of lightness. The light that reaches the eye and stimulates the photoreceptors is determined by both the light in the environment (e.g., sunlight) and the reflectance properties of the surfaces of the objects from which the light is reflected. Light at the eye can be measured in terms of its intensity, or its luminance. But people do not perceive luminance. Instead, they perceive surfaces as shades of gray (ignoring chromatic differences), which in turn is a representation of a surfaces reflectance properties. Lightness is the term used to refer to perceived surface reflectance. That is, lightness is the observer’s perceptual interpretation of what proportion of the incident light from the environment a given surface reflects. Surfaces that are perceived as reflecting relatively little light are perceived as dark gray or black. Surfaces that are perceived as reflecting a lot of light are perceived as light gray or white.

Address editorial correspondence to Anja Fiedler, 103 Spence Laboratories of Psychology, Department of Psychology, The University of Iowa, Iowa City, IA, 52242, USA. [email protected].

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The visual system computes lightness by taking into account scene-based information, such as the relative luminance of adjacent surfaces and the perceived illumination and transparency conditions of the scene. Are some objects in the shadow of other objects? Are some objects more directly under a light source than others? Is an object being viewed through some transparent material like glass, water, or fog? As a consequence contextual information plays a critical role in lightness perception. Imagine, for example, watching a white ball roll from sunlight into shadow. Although the amount of light reflected from the ball is much less once the ball reaches the shadow, we still perceive it as white. We do not perceive it as changing to gray as it rolls into the shadow. This phenomenon is referred to as lightness constancy: the tendency to perceive the lightness of surfaces as constant across different illumination conditions.

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Lightness perception is so dominant that it can be extremely difficult to recognize the actual luminance conditions. Consider, for example, the checkershadow illusion introduced by Adelson (1995) illustrated in Figure 1. In this illusion, a checkerboard is shown with a cylinder set on it and casting a shadow. When inspecting the left side of Figure 1, the square marked with an A seems to be darker than the square marked with B. The squares, however, are equiluminant. The context information provided by the checkershadow illusion (e.g., local contrast, perceived illumination, regularities of the checker board pattern) induces the perception of different lightnesses for the two surfaces. On the right side of Figure 1, the perceived difference in lightness is destroyed by the two superimposed gray bars that have the same luminance as squares A and B and connect them. Strikingly, even when we know that square A and square B are identical in terms of luminance, it is nearly impossible to perceive them as identical when re-inspecting the left side of Figure 1. Lightness overrides access to luminance.

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One view is that luminance information is unavailable because it is discarded at very early stages of information processing (see e.g., Gilchrist et al., 1994). This idea is consistent with the observation that subjective lightness is signaled as early as primary visual cortex within the visual system (Boyaci, Fang, Murray, & Kersten, 2010; MacEvoy & Paradiso, 2001; Pereverzeva & Murray, 2008), though it is unknown based on these studies alone whether or not feedback from anatomically later areas obscures evidence of luminance-specific signals. In addition to luminance, Robilotti and Zaidi demonstrated that lightness identification can be influenced by overall brightness (Robilotti & Zaidi, 2004) and contrast (Robilotti & Zaidi, 2006).

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In this study, we examined the role of luminance versus scene-induced lightness for the establishment and maintenance of object representations in dynamic scenes. Reconsider, for example, the white ball rolling into the shadow that was described above. The location and luminance of the ball change over time. This change in sensory input over time presents the visual system with the problem of computing object correspondence. Does the changing sensory information (new location, new luminance) reflect a new object in the scene or does it reflect the same object under different conditions at a later time? On the one hand, object correspondence is often resolved on the basis of spatiotemporal coherence. To the extent that a sequence of contrast signals (luminance, chromatic, texture, etc.) varies spatially and temporally in a manner that is consistent with a physically moving object, the system often

J Exp Psychol Hum Percept Perform. Author manuscript; available in PMC 2016 December 01.

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represents this ensemble of information as corresponding to a single object, rather than different objects (e.g., Flombaum, Scholl, & Santos, 2009; see also Kahneman, Treisman, & Gibbs, 1992; Pylyshyn, 2000).1 In addition to spatiotemporal information, however, the specific contrast information, or the surface-feature information, plays a role in determining object correspondence as well (Hein & Moore, 2012; Hollingworth & Franconeri, 2009; Moore, Stephens, & Hein, 2010; Richard, Luck, & Hollingworth, 2008; Tas, Dodd, & Hollingworth, 2012). There will be a tendency to perceive two stimuli sampled at different times as corresponding to a single object (rather than different objects) to the extent that those two stimuli share the same color, shape, size, or orientation. We asked whether lightness or luminance (or both) is used by the visual system to resolve object constancy when presented with changing values over time and space.

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A common method for assessing object correspondence is the object-reviewing paradigm (originally introduced by Kahneman, Treisman, & Gibbs, 1992). In one version of this paradigm (e.g., Hollingworth & Franconeri, 2009; Kimchi et al., 2013; Kruschke & Fragassi, 1996; Mitroff & Alvarez, 2007; Moore, Stephens, & Hein, 2010; Noles, Scholl, & Mitroff, 2005) two differently colored objects (e.g., squares) are presented to the left and to the right of fixation. Within each object, a preview stimulus (e.g., a letter) is presented briefly and participants are asked to keep those stimuli in mind. The two objects then move to new locations, and finally a stimulus again appears in each square. Participants indicate whether the final stimuli match those from the preview display or not. In case of a match, two different conditions are specified: In the congruent condition, the stimuli appear in the same (corresponding) objects as they did originally. In the incongruent condition, the matching stimuli appear in the opposite objects. Participants tend to respond faster in the congruent as compared to the incongruent condition. This congruency effect is referred to as object-specific preview benefit (OSPB) and is interpreted as an index of object correspondence. Specifically, it is assumed that a to-be-memorized stimulus is associated with its respective object during the preview display. If the stimulus reappears in the object to which it is already associated, the matching process and thus responses are more quickly and accurately compared to trials in which the stimulus appears in the opposite object. According to this interpretation, an OSPB should only be observed if a given object in the preview display and the corresponding object in the final display are perceived as being the same object over time. As soon as this perception of object correspondence is violated, no OSPB should be observed.

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Although OSPBs tend to occur for objects that are matched in terms of their spatiotemporal coherence across the moving portion of the display (Mitroff & Alvarez, 2007), surface feature information also plays a role (e.g., Hein & Moore, 2012; Hollingworth & Franconeri, 2009; Moore, Stephens, & Hein, 2010; Richard, Luck, & Hollingworth, 2008; Tas, Dodd, & Hollingworth, 2012). Most relevant for the current study, changing the feature information of the moving objects by, for example, having them change colors abruptly during the

1There are also many demonstrations of the dominance of spatiotemporal variables in the resolution of motion correspondence (e.g., Burt & Sperling, 1981; Kolers & von Grünau, 1976; Navon, 1976; Nishida & Takeuchi, 1990; Werkhoven, Sperling, & Chubb, 1993, 1994). There is reason to think, however, that motion and object correspondence processes are at least partially separable (Hein & Cavanagh, 2012; Moore & Hein, 2010a; Moore & Hein, 2010b; Moore & Hein, 2012). J Exp Psychol Hum Percept Perform. Author manuscript; available in PMC 2016 December 01.

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course of their motion to new locations, can eliminate the OSPB, suggesting that object correspondence is disrupted by the feature change (Moore, Stephens, & Hein, 2010). In the present study, we asked whether the OSPB depends on raw surface features like luminance or whether the OSPB depends on the perceived lightness of objects. From this we hoped to infer whether luminance, lightness, or both are factored into object correspondence processes. As outlined above, perceived lightness of objects’ is a combination of objects’ raw luminance and perceived illumination. We hence manipulated either scene-induced illumination conditions (Experiment 1) or objects’ luminance (Experiment 2).

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To manipulate illumination conditions, we combined the object-reviewing paradigm either with a plain gray background scene or with the checkershadow illusion illustrated in Figure 1. When objects’ moved on a plain gray background and their luminance switched, their lightness changes as well. There were no cues provided by the background that could account for the luminance switch (see movie 1). In line with Moore et al.’s (2010) findings, we expected to observe no OSPB for this condition. In contrast, the checkershadow display provides cues that imply two differently illuminated regions (one inside the shadow and one outside the shadow). By varying the luminance of objects within those two regions, one can elicit the perception of constant lightness or changing lightness. Consider an object that moves from one region to another (e.g., from inside the shadow to outside the shadow or vice versa). In this case, if luminance changes appropriately, then lightness will remain constant (see movie 2). If the OSPB depends on lightness, an OSPB should occur despite the switch in disks’ luminance.

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In Experiment 2, we manipulated disk luminance instead of the background scene. That is, we constantly used the checkershadow background scene and implied a change in illumination during the trial as the disks move from one illumination region to the other. In one condition, objects’ luminance switched in a way to support lightness constancy (compare Experiment 1). In the other condition, objects’ luminance stayed constant throughout the trial even though the illumination conditions changed. As a consequence, perceived lightness of the objects’ surface should change during the trial. Taken together, Experiments 1 and 2 allowed us to separate the potential influence of luminance and lightness on object correspondence, as measured in the object-reviewing paradigm.

Experiment 1 Author Manuscript

Experiment 1 used the object-reviewing paradigm to measure the influence of luminance and lightness on OSPBs in order to infer the respective roles of luminance and lightness in the perception of object correspondence. Objects were a light-gray and a dark-gray disk presented on either a plain gray background or on an informative background scene that depicted the checkershadow illusion. In the preview display, symbols were presented briefly in each disk. The disks then moved to new positions, at which point a symbol again appeared in each of the two disks. Observers reported as quickly and accurately as possible whether the two symbols in the final display were the same as those in the preview display.


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Method

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Participants—Sixteen students at the University of Iowa (2 male, mean age: 19.5 yrs; range: 18–21 yrs.; 3 left-handed) participated in Experiment 1 in exchange for researchparticipation credit in an introductory psychology course. Apparatus—Visual stimulus presentation was controlled by MATLAB software and the Psychophysics Toolbox extensions (Brainard, 1997; Pelli, 1997) running on a Mac computer. We used a 17-in. CRT color monitor (resolution: 1,024 × 1,280 pixels; refresh rate: 100 Hz) and fixed the viewing distance at 65 cm with the help of a chin rest. Participants used the left and the right shift keys (operated with their left and right index finger, respectively) on a standard computer keyboard for their responses.


Stimuli—For the plain gray condition, the background was set to a medium gray-value (34.5 cd/m2). For the checkerboard condition, eight versions of the checkershadow illusion were created by using the Blender open source 3D design software (Stichtung Blender Foundation, Entrepotdok 57A, 1018 AD Amsterdam, The Netherlands, http:// www.blender.org/). Each background image depicted a checkerboard (appr. 17.5° × 5° vis. angle) with a green cylinder (appr. 3° × 4° vis. angle) on top of it. There were four possible positions for the cylinder that in turn determined which region of the checkerboard was illuminated and which region was in the shadow: 1) cylinder in the front left casted a horizontal shadow on the front half of the checkerboard, 2) cylinder in the front right casted a horizontal shadow on the back half of the checkerboard, 3) cylinder in the back left casted a vertical shadow on the left half of the checkerboard, 4) cylinder in the back right casted a vertical shadow on the right half of the checkerboard. In addition, for each of the resulting four background images a resembling twin was created in which each white check was replaced by a black check and vice versa. The shadow was created by superimposing a transparent filter (70% filter; alpha value: 177) on the background images, using MATLAB and the Psychophysics Toolbox extensions (Brainard, 1997; Pelli, 1997; luminance values for checks outside of the shadow: white = 59.5 cd/m2; black = 33.8 cd/m2; checks in the shadow: white = 13.5 cd/m2; black = 8.2 cd/m2).

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Finally, a high-luminance disk (56.6 cd/m2) and a low-luminance disk (12.6 cd/m2) were superimposed on the background image and the filter. The luminance value of the lowluminance disk equaled the luminance value of the high-luminance disk altered by the filter. Consequently, a luminance switch from light to dark gray resembles the change in luminance that would result if the high-luminance disk would be altered by the filter (i.e., move from the illuminated area into the shadow). There were two different starting positions and four different movement paths employed for the disks. A virtual square (appr. 2° × 2° vis. angle) was centered on the screen and one disk started either on the top right or the top left of this virtual square. The other disks started diagonally opposite at the bottom left or bottom right of the virtual square. Disks moved either horizontally or vertically but always orthogonal to the shadow border. If disks moved vertically, their size and their movement path was adapted in order to account for perceived depth (i.e., disk diameter of lower disk: 0.8° vis. angle; disk diameter of upper disk: 0.6° visual angle). Furthermore, in both conditions we displayed a blue surfaces centered between the two disks. This surface acted


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as an occluder that was orthogonally oriented to the direction of disk movement in the current trial (horizontal occluder: 4 ° × 0.8 ° of vis. angle; vertical occluder: 0.8 ° × 2.6 ° vis. angle). The moving disks slid underneath it before reappearing in their new locations on the opposite side of the occluder. When the luminance switched between disks, the switch took place while the disks were entirely occluded. There was therefore no physical transient signal in any of the displays due to abrupt switch in disks luminance. For the matching task, symbols were randomly drawn from 21 possible Bodoni Ornaments. The symbols were presented either in a light-red font color (56.6 cd/m2; always presented in the light-gray disk) or in a dark red font color (12.6 cd/m2; always presented in the dark-gray disk).

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Procedure—The experiment consisted of one practice block (16 trials) and 12 experimental blocks with 32 trials each. The presentation of the scene background was blocked (plain gray vs. checkerboard) and the two block types alternated. Half of the participants started with a plain gray background and the other half started with a checkerboard background. One of the eight background images was assigned to each of the six checkerboard blocks based on a latin square design. In addition to the Background, we manipulated Congruency: In half of the trials, the two symbols in the preview display matched the two symbols in the final target display. In the other half of trials, one of the symbols did not match between preview and target display. Furthermore, in half of the matching trials, the symbols were presented in exactly the same disks (congruent match) and in the other half the matching symbols were presented in the opposite disks (incongruent match).

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The disks’ initial positions and movement paths were counterbalanced across trials (with the restriction that the disks always crossed the shadow border on the checkerboard background, that is they moved vertically when the shadow was oriented horizontally and vice versa). Overall, there were 384 experimental trials. Each trial started with the presentation of the two disks on either a plain gray background or on the checkerboard background image. For the checkerboard condition, the low-luminance disk was presented on the transparency matrix and thus perceived as lying in the shadow. In contrast, the high-luminance disk was never presented on the transparency matrix and thus perceived as being outside the shadow. After 500 ms, one symbol was presented in each of the disks for 1,000 ms. Then, the symbols disappeared and the disks moved 1.3 ° of vis. angle to their final positions within 450 ms. While the disks moved across the checkerboard, they disappeared behind the occluder and reappeared on its opposite side. Luminance switched between the two disks when the y were entirely covered by the occluder (21st frame or 210 ms of movement).

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When the disks reached their final position, symbols were again presented in each of the disks. Participants were asked to press the response key assigned to their dominant hand if the two symbols in the final display were the same as the two symbols of the preview display. If one symbol was different from those in the preview display, they were asked to press the response key assigned to their non-dominant hand. Furthermore, they were instructed to respond as quickly and as accurately as possible. The response terminated the trial and in case of an erroneous response, feedback (“Wrong key!”) was provided for 1,000


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ms. The next trial started after an intertrial interval of 1,000 ms duration. Feedback about the remaining number of blocks was provided after each run of 32 trials. In addition participants could take a short rest before they initiated the next block of trials with a key press. Results Mean response time (RT) and error rate (ER) are shown in Figure 2. There was a significantly reversed OSPB when disks moved on a plain gray background. This replicates previous findings showing that OSBPs are disrupted and can even reverse when surface features change abruptly (Moore, Stephens, & Hein, 2010). In contrast, when the disks moved on the checkerboard background an OSPB did occur. Statistical analyses of the data confirm this summary.

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Experiment 1: RT Data—Only RTs from correct matching trials that did not exceed more than 3 standard deviations of that participant’s mean RT in each condition (no more than 1.12% of the data were discarded as outliers for each experiment reported in the following) were analyzed. A 2 × 2 repeated measures analysis of variance (ANOVA) with the factors Congruency (congruent match vs. incongruent match) and Background (plain gray vs. checkerboard) was performed on participants’ mean RTs (that was Greenhouse-Geisser corrected where necessary). Neither the factor Congruency (F < 1) nor the factor Background (F(1,15) = 2.16, MSE = 9,316, p > .05) revealed significant main effects. Importantly however, there was a significant interaction between Congruency and Background, F(1,15) = 19.50, MSE = 2,448, p < .005, partial η2 = 0.56.

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To further investigate this interaction, paired t-tests were performed to examine the effect of the factor Congruency (i.e., the OSPB) in the two background conditions separately. The OSPB was significant in the checkerboard background condition, t(15) = 5.26, p < .001, r2 = 0.65, whereas it was reversed in the plain background condition, t(15) = 2.37, p = .031, r2= 0.27.

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Experiment 1: Error Data—A 2 × 2 ANOVA with the within-subjects factors Congruency and Background was performed on arc sine transformed error rates. There was no effect of Congruency (F < 1). However, participants responded more accurately in the checkerboard condition (15 %) than in the plain gray condition (19 %), F(1,15) = 10.0, MSE = 0.021, p = .006. The interaction between Congruency and Background on error rates was significant, F(1,15) = 13.4, MSE = 0.027, p = .002. This interaction was further analyzed with paired t-tests. They revealed no significant OSPB for the checkerboard condition, t(15) = 1.8, p = .091. However, the OSPB was significantly reversed for the plain gray condition, t(15) = 2.2, p = .047. Discussion Experiment 1 contrasted the influence of luminance versus lightness on the OSPB. When objects were presented on an uninformative plain gray background, a switch in luminance resulted in a reversed OSPB. This finding is in line with the results reported by Moore et al. (2010) who observed a reversed OSPB when objects switched their colors. Crucially, the same switch in luminance between the two objects resulted in a reliable OSPB when objects


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were presented on the checkerboard background. The checkerboard background provided information about illumination conditions, which can account for the switch in luminance. That is, when the disks moved from one illumination condition to the other, the luminance switch corresponded to the inferred change in illumination and thus objects’ lightness was constant. We would like to emphasize that the background scene constitutes the only difference between the two conditions tested here. Given that the objects (i.e., disks) themselves are identical in both conditions, it is striking that the results differ largely between the two of them.

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To the extent that OSPBs provide an index of object correspondence, these results suggest that object correspondence was determined by lightness. Lightness in turn, was solely induced by the informative background scene of the checkerboard. We hence argue that the OSPB is not only influenced by objects’ spatiotemporal and/or local surface features. Moreover, cues provided by a context scene (here, perceived illumination) do interact with objects’ surface features (here, luminance) and can thus affect the occurrence of the OSPB as well. In a next step, we wanted to confirm this finding by choosing a different approach to influence objects’ lightness. Instead of manipulating the background scene, we manipulated disks’ luminance in Experiment 2. Specifically, we replicated the checkerboard condition of Experiment 1 and contrasted it with a condition in which disks’ luminance stayed constant throughout the trial.

Experiment 2 Author Manuscript

In Experiment 2, we manipulated disk luminance (switch vs. no switch) while presenting the checkerboard background scene in each trial. When luminance switches between objects’, it could be accounted for by the change in scene-based illumination conditions and objects’ lightness should be perceived as remaining constant. This condition is a direct replication of the checkerboard condition in Experiment 1 and we expect to obtain a reliable OSPB. In contrast, when luminance stays constant but the illumination conditions change as the disks move, the lightness of the disks changes dramatically (see movie 3). Thus, if lightness is information drives the OSPB, there should be no OSPB observed when luminance stays constant and lightness changes. Method

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A new sample of sixteen students of the University of Iowa (1 male, mean age: 19.2 yrs; range: 18–21 yrs.; 3 left-handed) participated in exchange for partial fulfillment of a course requirement. Stimuli and procedure were virtually identical to the ones in Experiment 1 with two exceptions: First, we used the checkerboard background in both experimental conditions. Second, we manipulated disks’ luminance and compared one condition in which luminance stayed constant throughout the trial with one condition in which luminance switched between disks (compare Experiment 1).


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Results

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Mean RT and error rates from Experiment 2 are shown in Figure 3. There was an OSPB when luminance switched between disks between the preview and test displays. In addition, we also observed an OSPB when luminance remained constant over the course of the trial. RT Data—A 2 × 2 ANOVA (Greenhouse-Geisser corrected where necessary) on participants’ mean RTs revealed a significant main effect of the factor Congruency, F(1,15) = 22.7, MSE = 3,081, p < .001, partial η2 = 0.60, indicating that participants responded faster in the congruent than in the incongruent condition. Furthermore, participants were faster when luminance switched between disks as compared to the condition in which luminance remained constant, F(1,15) = 29.7, MSE = 1,363, p < .001, partial η2 = 0.66. Finally, there was no significant Congruency x Luminance interaction, F(1,15) = 1.2, MSE = 1,755, p > .05.

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Error Data—The 2 × 2 ANOVA on arc sine transformed error rates revealed a significant main effect of the factor Congruency, F(1,15) = 10.47, MSE = 0.021, p = .006. Participants responded more accurately in the congruent than in the incongruent condition. There was a significant main effect of Luminance, F(1,15) = 11.61, MSE = 0.036, p = .004, indicating that participants responded more accurately when luminance switched between disks than when luminance stayed constant throughout the trial. There was no significant interaction, F(1,15) = 2.89, MSE = 0.015, p > .05. Discussion

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Experiment 2 again contrasted the influence of luminance versus lightness on the OSPB. Based on the findings of Experiment 1, we expected to observe an OSPB when the disks’ lightness remained constant and no OSPB when the disks’ lightness changed. In contrast to Experiment 1, we induced lightness differences by manipulating objects’ luminance (switch vs. no switch) while using the same background scene depicting the checkershadow illusion for each condition. When luminance switched between objects’ the switch corresponded to the change in illumination and should result in the perception of constant disk lightness. In this condition, we observed a reliable OSPB, which is in line with the findings of Experiment 1. This further suggests that lightness information rather than raw luminance seems to influence object correspondence as measured by the object-reviewing paradigm.

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However, in contrast to our expectations, we also observed a reliable OSPB even when objects’ luminance remained constant. This was unexpected because when the objects’ luminance stayed constant across large changes in perceived illumination conditions, the objects’ lightness usually changes dramatically. This is hard to reconcile with the claim that the OSPB depends on lightness information as suggested by the findings of Experiment 1. Summarizing our results so far, one might argue that the presentation of a background scene always resulted in an OSPB independent of whether the disk luminance switches or not. However, we propose an alternative interpretation. We suggest that the influence of the informative background scene on the objects depends on whether they are both perceived as belonging to the same illumination frame of reference (Kardos, 1934; Koffka, 1935;


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Radonjic & Gilchrist, 2013; Zdravkovic, Economou, & Gilchrist, 2011). In contrast, if the objects and the checkerboard scene are perceived as lying on different depth planes and thus belonging to different illumination frames of reference, then scene-based contingencies are not implemented in the interpretation of this scene-independent object. The visual system might use various cues within a scene to decide whether an object belongs to a background scene or not. In Experiment 2, when the two disks did not change their luminance despite the background scene changes in illumination (see movie 3), this might have served as a strong cue indicating that the two disks were not a part of that scene. Instead, one might perceive the two disks as moving on a depth plane closer to the observer instead of moving on the checkerboard. In this case, a change in illumination implied by the scene would have no consequences for the luminance of the disks. Thus, when disks luminance remains constant throughout the trial and changing illumination conditions are not interpreted as affecting the disks, an OSPB should still be observed.


In order to test this post-hoc explanation of our results, we designed a condition which fulfilled two prerequisites: First, we introduced a switch in luminance between the two disks that could be accounted for by changes in the illumination conditions as implied by the background scene. Under the belongingness hypothesis, if the disks are perceived as belonging to the scene, an OSPB will occur. If they are not, no OSPB will occur. Thus, the critical manipulation was to introduce cues that suggested that the disks were separate from the background scene. To this end, we designed three experiments that closely resembled Experiment 2. That is, we used the checkerboard background scene and compared a condition in which the luminances of the disks remained constant and compared it with a condition in which luminances switched between disks. In addition, we introduced cues signaling a violation of object-scene binding. Specifically, in Experiments 3 and 4 we manipulated the luminance of the symbols that were presented on the disks. Those symbols are the basis of the matching task that the participants perform and they are interpreted as being associated with their respective object. We reasoned, that using symbols that are unaffected by the scenes illumination conditions (i.e., their luminance was invariant) might perceptually separate the object and background scene. If this is the case, we expect to not observe an OSPB if disks luminance switches although the scene-based illumination conditions could account for the luminance switch. In Experiment 3, we additionally removed the occluder from the display to expose the participants to the transient signal that is present when luminance abruptly switches between objects. The results of both experiments are consistent with the belongingness hypothesis according to which objects and scene have to be perceived as belonging to the same illumination reference frame in order to observe scene-induced effects in the object-reviewing paradigm.

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Experiments 3 and 4 In Experiments 3 and 4, we used the checkerboard background and compared a condition in which the disks’ luminances remained constant over the trial with a condition in which luminance switched between disks during the trial. So far, this closely resembles our manipulation in Experiment 2. However, in addition we introduced cues that were intended to encourage a separation of objects and scene. In Experiment 3, we did not present an occluder. Hence, when disks’ luminance abruptly switched, there was a physical transient


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signal visible. Furthermore, we presented bright red symbols on the disks that did not change in luminance across the different illumination conditions. That means, that the symbol presented on a disk outside of the shadow would have the same luminance as the symbol that is presented on a disk inside the shadow. This failure to change in luminance across illumination conditions should be a powerful cue implying that the disks are separate from the background scene. We expected to observe an OSPB when luminance remained constant, but no OSPB when luminance switched between disks. This result would be consistent with the hypothesis that objects have to be perceived as belonging to the background scene for enabling scene-induced effects on the OSPB. Finally, Experiment 4 was a replication of Experiment 3 that was identical in design except that the occluder was included as in previous experiments. Method

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A new sample of sixteen students participated in Experiment 3 (8 female, mean age: 19.5 yrs; range: 18–21 yrs.; 2 left-handed), and another new sample of sixteen students participated in Experiment 4 (8 female, mean age: 19.7 yrs; range: 18–23 yrs.; 2 lefthanded). Stimuli and procedure were virtually identical to the ones in Experiment 2 with the following exceptions: We used the same luminance for the symbols’ font (35 cd/m2) independent of whether the disks were presented inside or outside the shadow. Furthermore, in Experiment 3 there was no occluder presented, thus when luminance abruptly switched between disks from one frame to the other, there was a physical transient. Results

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Mean response time (RT) and error rate (ER) from Experiments 3 and 4 are shown in Figures 4 and 5, respectively. In both experiments, there was a large OSPB when disk luminance remained constant across the trial sequence. That effect was absent however, when the luminance values switched between disks over the course of the trial. Statistical analyses of the data confirm this summary. We present the analyses for RT and ER for each experiment separately.

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Experiment 3: RT Data—A 2 × 2 repeated measures analysis of variance (ANOVA) with the factors Congruency (congruent match vs. incongruent match) and Luminance (no switch vs. switch) revealed shorter RT in the congruent as compared to the incongruent condition, F(1,15) = 40.21, MSE = 2,543, p < .001, partial η2 = 0.73. Furthermore, participants responded faster when luminance switched between disks as compared to when luminance did not switch, F(1,15) = 8.3, MSE = 2,117, p = .011, partial η2 = 0.37. The Congruency x Luminance interaction reached significance, F(1,15) = 18.37, MSE = 5,599, p = .001, partial η2 = 0.55: the OSPB was significant in the no luminance switch condition, t(15) = 6.03, p < . 001, r2= 0.71, but not in the luminance switch condition, t(15) = 0.01, p > .05, (compare Figure 4). Experiment 3: Error Data—The 2 × 2 ANOVA on arc sine transformed error rates revealed neither a significant main effect of the factor Congruency, F(1,15) = 3.1, MSE = 0.015, p = .1, nor of Luminance (F < 1). There was, however, a significant Congruency x Luminance interaction, F(1,15) = 17.64, MSE = 0.039, p = .001: An OSPB was observed in


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the no luminance switch condition, t(15) = 5.1, p < .001, that was significantly reversed in the luminance switch condition, t(15) = 2.4, p = .031. Experiment 4: RT Data—A 2 × 2 ANOVA (Greenhouse-Geisser corrected where necessary) on participants’ mean RTs revealed a significant main effect of the factor Congruency, F(1,15) = 15.6, MSE = 3,703, p = .001, partial η2 = 0.51. Participants responded faster in the congruent than in the incongruent condition. There was no significant main effect of Luminance, F(1,15) = 2.11, MSE = 4,686, p = .17, but a significant Congruency x Luminance interaction, F(1,15) = 32.73, MSE = 4,771, p < .001, partial η2 = 0.69. Additional t-tests revealed that the OSPB was significant in the no luminance switch condition, t(15) = 6.63, p < .001, r2= 0.75, but not in the luminance switch condition, t(15) = 1.76, p = .1.

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Experiment 4: Error Data—The 2 × 2 ANOVA on arc sine transformed error rates revealed a significant main effect of the factor Congruency, F(1,15) = 25.18, MSE = 0.022, p < .001. Participants responded more accurately in the congruent than in the incongruent condition. There was no significant main effect of Luminance (F < 1). However, a significant Congruency x Luminance interaction, F(1,15) = 53.98, MSE = 0.029, p < .001, reflected an OSPB in the no luminance switch condition, t(15) = 9.56, p < .001, that was absent in the luminance switch condition, t(15) = 2.06, p = .058. Discussion

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The goal of Experiments 3 and 4 was to test the hypothesis that objects must be perceived as being part of the scene in order for the scene to influence the OSPB. To this end, we focused on the case in which a switch in objects’ luminance could be accounted for by the implied illumination conditions if the objects are perceived as belonging to the scene. Additional cues, however, were included to discourage that perception. Consistent with the hypothesis, we observed a large OSPB when the disks luminances stayed constant over the trial but no OSPB occurred when disk luminances switched between disks. That is, OSPBs were determined by luminance rather than lightness. This contrasts with Experiments 1 and 2, in which more cues suggested that the disks were part of the scene and OSPBs were determined by lightness rather than luminance.

General Discussion

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The present study investigated the role of luminance versus scene-induced lightness in the establishment and maintenance of object representations in dynamic scenes. The strategy was to combine the object-reviewing paradigm (Kahneman, Treisman, & Gibbs, 1990) with the checkershadow display (Adelson, 1995). Object-specific preview benefits, as measured in the object-reviewing paradigm, are often used as an index of object correspondence (Kahneman, Treisman, & Gibbs, 1990; Mitroff & Alvarez, 2007). That is, if an OSPB occurs for two stimuli, those two stimuli are interpreted as representing a single object over time. Presenting stimuli within the context of the checkershadow display allowed us to separately assess whether an object’s luminance or an object’s lightness has an effect on the OSPB.


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In Experiment 1, we established that a switch in objects’ luminance can eliminate the OSPB when the objects are presented in front of a uniformly colored background. This is in line with the findings of Moore et al. (2010) who observed no OSPB when objects’ color switched during the trial. Strikingly, when an informative background scene was added in the present study, the same switch in the objects’ luminance resulted in a reliable OSPB. The background scene was designed to provide regions of different illumination conditions which could account for the change in luminance of the moving objects and support lightness constancy. Thus, the results suggested that the OSPB is determined by objects’ lightness, which in turn is a combination of luminance and scene-based information, rather than just luminance.


In Experiment 2, we replicated the finding of Experiment 1 and observed an OSPB for moving objects that switched their luminance but remained constant in lightness due to the checkerboard background scene. However, an OSPB also occurred when the objects moved to different illumination areas without changing their luminances accordingly, that is, a disruption in lightness failed to disrupt the OSPB. This result was unexpected, because a violation of lightness constancy should have eliminated the OSPB if the OSPB indeed depends on lightness information. To account for this finding, we introduced the concept of illumination reference frames (Kardos, 1934; Koffka, 1935; Radonjic & Gilchrist, 2013; Zdravkovic, Economou, & Gilchrist, 2011). Specifically, we hypothesized that in order for scene information to influence the OSPB, objects must be perceived as being a part of the scene. This perceived belongingness might have been disrupted in Experiment 2, when objects maintained their luminance despite changing illumination conditions. The results of Experiments 3 and 4 provided support for this hypothesis. We used the same displays as in Experiment 1 and 2 and that resulted in reliable OSPB. However, we introduced cues that contradicted the interpretation that the objects were part of the background scene. Specifically, we presented symbols on the respective objects that did not adapt their luminance when under different illumination conditions. The symbol-based information is hence in sharp contrast to the interpretation that the disks including the symbols presented on them are affected by the scene-induced illumination conditions. This manipulation of symbol luminance eliminated the OSPB and thus supports the idea that the perceived belongingness of the objects to the scene determines whether cues provided by the scene are taken into account and can influence the OSPB.

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Although the aim of the present study was to investigate the role of luminance and lightness for object correspondence in the object-reviewing paradigm, the conclusions of the present results go beyond that: The visual system uses various cues in order to derive meaning from the changing and sometimes conflicting sensory information. One of its tasks is to decide whether changing visual information reflects the same object over time and using OSPBs as an index of that, it has been shown that object correspondence relies on cues like spatiotemporal coherence as well as on objects’ surface properties (e.g., Hollingworth & Franconeri, 2009; Moore, Stephens, & Hein, 2010; Richard, Luck, & Hollingworth, 2008). In the present study, we demonstrated that perceived lightness derived from scene-based information can also serve as a cue for object correspondence. Another task of the visual system is to decide whether objects are a part of a background scene. If they are, then their representations will be influenced by the scene conditions. If they are not, then their J Exp Psychol Hum Percept Perform. Author manuscript; available in PMC 2016 December 01.

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representations will be unaffected by the scene conditions. We conclude this because when cues implied a separation of objects and background scene (Experiments 3 and 4), OSPBs were unaffected by background information. When cues implied that the objects were part of the scene, OSPBs were influenced by background information. In summary, the results of the present study rule out the hypothesis that object correspondence, as indexed by the OSPB, is determined by luminance alone. Instead, they are consistent with the hypothesis that it is determined by lightness, as implied by scene information. Critically, however, for scene information to influence object correspondence, the object must be represented as being part of the scene.

Supplementary Material Refer to Web version on PubMed Central for supplementary material.

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Acknowledgments This study was supported by the Deutsche Forschungsgemeinschaft (FI 1924/1-1) and by NIH R21 EY023750.

References


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Author Manuscript Figure 1.

The checkershadow illusion first published by Adelson in 1995. Left: The checks A and B are equiluminant but their perceived lightness differs. Right: Superimposition of two bars in the same shade of gray destroys the illusion. ©1995, E.H. Adelson

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Author Manuscript Author Manuscript Figure 2.

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Mean reaction time (RT in ms) error rates (Error in %) as a function of Congruency (same object vs. different objects) and Background (plain gray vs. checkerboard) in Experiment 1. Error bars show the mean ± standard error using the algorithm for within-subject designs recommended by Cousineau (2005).

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Mean reaction time (RT in ms) error rates (Error in %) as a function of Congruency and Luminance in Experiment 2. Error bars show the mean ± standard error using the algorithm for within-subject designs recommended by Cousineau (2005).

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Mean reaction time (RT in ms) error rates (Error in %) as a function of Congruency (same object vs. different objects) and Luminance (no switch vs. switch) in Experiment 3. Error bars show the mean ± standard error using the algorithm for within-subject designs recommended by Cousineau (2005).


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Mean reaction time (RT in ms) and error rates (Error in %) as a function of Congruency (same object vs. different objects) and Luminance (no switch vs. switch) in Experiment 4. Error bars show the mean ± standard error using the algorithm for within-subject designs recommended by Cousineau (2005).


Standard deviation of luminance distribution affects lightness and pupillary response.

Facilitation of pattern recognition by cuing foveation with the luminance centroid as origin of the frame of reference.

Depth effect on lightness revisited: The role of articulation, proximity and fields of illumination.

Luminance gradient configuration determines perceived lightness in a simple geometric illusion.

Spatial reference frame of attention in a large outdoor environment.

The effective reference frame in perceptual judgments of motion direction.

Linear tuning of gamma amplitude and frequency to luminance contrast: evidence from a continuous mapping paradigm.

Reference-frame specificity of perceptual learning: the effect of practice.

Visual field differences in perception of the vertical with and without a visible frame of reference.

3D-MAD: A Full Reference Stereoscopic Image Quality Estimator Based on Binocular Lightness and Contrast Perception.

Unified frame of reference improves inter-subject variability of seismocardiograms.

From a Somatotopic to a Spatiotopic Frame of Reference for the Localization of Nociceptive Stimuli.

Deep mantle structure as a reference frame for movements in and on the Earth.

The Human Retrosplenial Cortex and Thalamus Code Head Direction in a Global Reference Frame.

Reference frame selection in dialog: priming or preference?

Use of Occlusal Splint for Noninvasive Fixation of a Reference Frame in Orbital Navigation Surgery.

Hemispheric differences in the perception of lightness.

Validation of reference materials for uranium radiochronometry in the frame of nuclear forensic investigations.

Generalization of Dexterous Manipulation Is Sensitive to the Frame of Reference in Which It Is Learned.

external frame of reference model using grades and test scores.

An online paradigm for exploring the self-reference effect.

Can you experience 'top-down' effects on perception?: The case of race categories and perceived lightness.

On Being the Same in Different Places: Evaluating Frame-of-Reference Effects Across Two Social Contexts.

Egocentric reference frame bias in the palmar haptic perception of surface orientation.