Prehatch Color Stimulation Effects on Color Pecking Preferences and Color Discrimination Learning in White Leghorn Chicks GLORIA J. FISCHER STEPHEN J . DAVIS JOHN A. NORD Department of Psychology Washington State University Pullman, Washington
Four experiments assessed the effects of stimulating chick embryos with colored light at 2 intensity levels. Both posthatch color pecking preferences (Experiments 1 and 2) and color discrimination learning (Experiments 3 and 4)were unaffected. These results affirm and extend a prior finding of no pre- and posthatch colored light stimulation effect on posthatch color preferences in ducklings. The color pecking preferences found replicated prior findings with chicks. However, they djffered from the approach color preferences observed in color discrimination learning.
Visually evoked responses of duck embryos and hatchlings recorded electrophysiologically are modified by prior exposure to light (Paulson, 1965). However, little evidence exists that prehatch light stimulation affects posthatch perception. For example, chicks from eggs exposed to one of several rates of visual flicker on Day 19 of incubation showed no enhanced posthatch responsiveness to that rate. Unexpectedly, chicks exposed to relatively rapid flicker rates (i.e., 1.2 or 3.5 fps) showed enhanced responsiveness to the rate they had not been exposed to (Dimond & Adam, 1972). Oppenheim (1968), on the other hand, found no effects whatsoever from direct stimulation of duck embryos with white or yellow light for 30 hr prior to hatching and for another 20 hr after hatching. These ducklings appeared to be less fearful than dark-hatched ducklings, but their magnitude of pecking and color pecking preferences were unaffected. Because ducklings have a very pronounced and nearly exclusive preference for green, modification of their color preferences might be especially difficult. Chick color preferences, on the other hand, are much less pronounced (e.g., Fischer, Morris, & Ruhsam, 1975) and, thus, seemed more amenable to possible modification. However, the present studies showed that, similar to the manipulation of ducklings, prehatch colored light stimulation failed to affect the magnitude of pecking preferences or color discrimination learning in the White Leghorn chick. Received for publication 4 December 1974 Revised for publication 7 February 1975 Developmental Psychobiology, 8(6): 525-531 (1975) 0 1975 by John Wiley & Sons, Inc.
525
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Experiments 1 and 2: Prehatch Color Stimulation and Posthatch Color Pecking Preferences Method
Subjects A total of 181 1-day-old White Leghorn chicks (Gallus domesticus), hatched from 16 weekly hatchings, were used in Experiment 1.
Apparatus Prehatch Light Stimulation. The top of a forced-air incubator was replaced with a combination filter, diffusion grid, and light-source enclosure. The color filters (30.5 x 30.5 cm) were compound filters with peak wavelengths of 450 nm (blue), 545 nm (green), and 650 nm (red), and were nonoverlapping, i.e., had half bandwidths of 40 nm, 45 nm, and 45 nm, respectively. The light sources were incandescent bulbs; light intensity could be varied with a rheostat. The intensity at the egg (33 cm below the filter) was measured with a Macbeth illuminometer. The calculated intensity reaching the embryo (accounting for absorption by the transparent tape window and inner egg membrane) was .0518 cd/cm2. For a control (no prehatch light stimulation) condition a filter was not used, but, because the compound filters transmitted infrared, an infrared source (a 350-ohm ceramic resistor) was mounted in the light sockets with the rheostat adjusted to full intensity. Timers regulated the daily light cycle from 0600 hours to 1800 hours with a 3-per-see flickering light (see Kovach, 1970) “on” for 90 sec and “off’ for 180 sec. This on-off sequence totaled 4 hr of light per day. Color Pecking Preferences. The color pecking preference test apparatus and optical calibration have been described by Fischer et al. (1975). Briefly, it consisted of 4 chambers each with a pecking key, filter holder, light source, and counter. A key peck of 5/g pressure activated a microswitch connected to a counter. The light source was a Bausch and Lomb 100-W, variable iris, microscope illuminator. A Photovolt Corporation monochromatic filter could be mounted between each key and its light source. The blue (437 nm), green (541 nm), and red (653 nm) interference filters used for testing pecking preferences were selected to correspond as closely as possible with the peak wavelengths of the filters used for stimulating embryos. An orange (594 nm) filter also was used in testing pecking preferences. Half bandwidths determined with a Beckman Spectrophotometer were 11.5 nm (blue), 8.5 nm (green), 9.0 nm (orange), and 12.5 nm (red). The test chambers were located in a darkened room. Thus, when the illuminators were on, only a .3-cm spot on each key was visible. An arbitrarily selected key, filter (594 nm), and projector were the designated standard. The intensity of the orange target in this standard projector was adjusted, using the projector iris, to .00056 cd/cm2, as measured with a Macbeth illuminometer, 35.6 cm from the key’s surface, This standard intensity was then used to calibrate a Photovolt Corporation 520M Photometer (whch gives an essentially flat response to the radiant energy of the wavelengths used in the present study). The photometer was used, in turn, t o equilibrate the radiance of the 4 different key/light-source combinations. During calibration the photometer was frequently recalibrated against the standard optical system.
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527
Procedure Incubation, Light Stimulation, and Hatching. Weekly hatches of fertile eggs were set in a commercial incubator for 14 days; then a I-cm square was cut out of each egg shell toward the air sac end (approximating the head position of the embryo). Cutting these holes required removing a piece of shell and the underlying shell membrane without damaging the inner membrane. The holes were covered with transparent tape, and the eggs placed on the top tray of the light stimulation incubator. The holes faced upward toward the light enclosure and source. Timers were activated so that the light stimulation schedule began at 0600 hours on the 15th day of incubation and continued through 1800 hours on the 20th day. The stimulation consisted of flickering (3 fps) red, green, or blue light or infrared (i.e., no light control). At the completion of the stimulation cycle on the 20th day (i.e., after 1800 hours) the eggs were hatched in darkness. Color Pecking Preference Tests. The chicks were tested in sets of 4 when their average age was 24 hr with an age range < 4 hr. They were placed randomly in the 4 test cubicles, facing the pecking key, and 5 min later the light sources were turned on for the 1st of four 15-min pecking sessions. During 5-min intersession intervals, the number of pecks were recorded, and the illuminator iris setting and color filter behind each key were changed. This was done with a board placed over all 4 chambers so that the subject would be in darkness. Thus, the only light source visible to the chicks at any time prior to or during testing was the color spot on the pecking key. Each chick was exposed to all 4 filters colors (blue, green, orange, and red) in a random order over the 4 pecking sessions.
Results and Discussion Seventeen (9%) of the 181 subjects tested did not peck at any filter color over the 4 test sessions and were discarded. For the remaining 164 the mean number of pecks per filter color in each of the prehatch light stimulation conditions was analyzed using a 4 x 4 (Prehatch Color x Posthatch Test Color) repeated measurements design analysis of variance. Results revealed no Prehatch Color effect on either the magnitude of pecking or on color pecking preferences (F’s< 1.0 for Prehatch Color and its interaction with Posthatch Test Color). Overall differences in color preferences did exist (F = 4.8 1, df= 3/48; p < .01; see Fig. 1). Individual F tests revealed that blue was preferred over green and red ([blue vs red]) F = 4.1 1, df = 1/41, p < .05). Orange was preferred over green ( F = 6.83, p < .Ol), but was not quite significantly preferred over red ( F = 3.52, 1.0 > p > .05). Taken together, blue and orange clearly were preferred over green and red, also taken together ( F = 10.8, p < .Ol). These preferences are in complete agreement with color preferences of dark-hatched clucks reported in Fischer et al. (1975). The intensity of prehatch light stimulation in Experiment 1 could have been insufficient to produce posthatch effects on color preferences. Therefore, experiment 1 was replicated on another 120 subjects in Experiment 2 with a 3-fold increase in the intensity of the prehatch light stimulation and twice the total daily amount. Specifically, the intensity of prehatch illumination calculated as in Experiment 1 with the blue filter was increased from the -0518 cd/cm2 in Experiment 1 to .I555 cd/cm’. The duration of prehatch light stimulation was doubled by reversing the 1.5-min on:3-min off ratio in Experiment 1 to a 3-min on: 1.5-min off ratio. Th~sreversal increased the total amount of light stimulation per day from 4 hr to 8 hr. Results again showed no significant effect due
528
FISCHER, DAVIS, AND NORD
Prenotch Treatment &--.A
Red ( 6 5 0 n m )
o----O Green ( 5 4 5 n m ) &--+ Blue ( 4 5 0 n m ) S--* No Light
541
594
653
Wavelength in Nanometers
Fig. 1. The mean number of pecks per filter color by chicks in prehatch color and no-light stimulation groups.
to Prehatch Color stimulation (F’s < 1.0 for Prehatch Color and its interaction with Posthatch Test Color), but again color preferences differed significantly (F = 10.4, df = 3/35, p < .Ol). Specifically, the differences found in Experiment 1 (see Fig. 1 ) were replicated and, in fact, accentuated. These accentuated differences in color preferences may have been due to an increase in the absolute amount of pecking, especially in prehatch light groups. If the absolute amount of pecking were related, in turn, to the increased intensity of prenatal light used in Experiment 2, the effects of prehatch sensory stimulation (see also Fischer, 1974) would appear t o be nonspecific rather than specific. Based on results of Experiments 1 and 2, we conclude that the prehatch intensities and wavelengths used did not affect embryos such that their posthatch color preferences were changed. A discrimination task, however, might be a more sensitive measure of prehatch color stimulation effects. This possibility was tested in Experiments 3 and 4. Experiment 3 compared blue, green, white, and no prehatch light stimulation groups on posthatch learning of a blue.green light discrimination in a Y-maze. The inclusion of a white-light control group was to insure that possible enhancement effects of prehatch color stiniulation on color discrimination learning could be attributed t o hue, as opposed to light stimulation, per se.
Experiments 3 and 4: Prehatch Color Stimulation and Posthatch Color Discrimination Learning Method The selection of subjects in Experiment 3 (143 White Leghorn chcks hatched from 12 weekly settings), and the apparatus and procedure for prehatch light stimulation followed that of Experiment 1 with one exception: the additoin of a white-light control (incandescent bulbs only) group.
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529
Color discrimination training was conducted in a Y-maze in a 10°C temperaturecontrolled cold room. The Y-maze had optical and heat systems at the end of each alley. Each optical system consisted of a microscope illuminator (those used in Experiments 1 and 2), color filter, and 2 mirrors to project a 2.54-cm square of color onto the goal box end wall. Filters were mounted in movable holders and had peak wavelengths of 437 nm (blue) and 541 nm (green) with half bandwidths of 11.5 nm and 8.5 nm. respectively. The intensity of the projected colors was equilibrated (using the same procedure and instruments as with the pecking apparatus) at .0085 cd/cm2. Each heat system consisted of a 250-W heat lamp and an infrared filter that transmitted no visible light into the maze. Both heat lamps could be activated simultaneously by a 20-sec timer. Six pairs of chicks, closely matched for age, were tested weekly. Half, randomly selected, learned the blue-green discrimination with blue positive, and the other half had green positive. In this manner 18 subjects were run in each of the 8 combinations of rewarded color (blue or green) and prehatch light stimulation condition (blue, green, white, or none). Each pair of chicks was run in tandem on the blue-green task; each received 6 blocks of correction trials: 7 trials onBlocks 1-3at average pair ages of 22,24, and 26 hr, and 9 trials per block on Blocks 3-6 at ages 44,46, and 48 hr. Entrance into (or, on correction trials, prodding into) the correct end box activated the timer for 20 sec of heat reward. During a 3-min intertrial interval, each chick was returned to a holding box while the other was tested. The position of the correct goal box was varied randomly for each pair. Between blocks of trials, subjects were kept in a darkened 29°C room. Thus, posthatch light experience was restricted to the blue and green light visible during learning trials.
Results and Discussion The number of correct choices per chick per trial block was converted to a percent correct score whch showed heterogeneity among between-group variances (xz = 31 3,df = 7, p < .Ol). An arcsin J p transformation of initial (Block 1) and terminal (Block 6) percentages reduced this heterogeneity to an acceptable level (x' = 113,df= 7, p < .12). These transformed data were analyzed using a 4 x 2 x 2 (Prehatch Light Stimulation groups [blue, green, white, or none] x Positive Stimulus Color [blue or green] x Trial Block [l and 61) repeated measurements design analysis of variance. Results showed 2 significant effects (see Table 1): increased learning over trials ( F = 424.4, df = 1/135, p < .Ol), and better learning when the positive color was green than when it was blue (F = 14.1, df = 1/135, p < .Ol). The latter difference (see rewarded color means in Table 1) was clearly related to an approach preference for green over blue, in that the chicks chose green over blue rather consistently, even on early trial blocks. The Prehatch Light Stimulation effect approached significance (F = 2.46, df = 3/135, p < .06), but the trend reflected a somewhat negative effect on learning from prehatch white stimulation rather than any enhancement effect from prehatch color stimulation. For example, overall mean percent correct responses for prehatch no-light, blue, green, and white light groups were 71.7, 70.3, 73.9, and 66.7, respectively. As in Experiment 1, the failure in Experiment 3 to show a Prehatch Color Stimulation effect could have been due to insufficient light intensity. Thus, another 117 chicks received prehatch blue, green, or no light at the higher (.1555 cd/cm2) intensity used in Experiment 2. Results from Experiment 4 were quite similar to those of
530
FISCHER, DAVIS, AND NORD
TABLE. I . Mean Percent Correct Responses on First (1)and Last ( 6 ) Trial Blocks on a Blue-Green Discrimination us a Function of the Rewarded Color. Trial Block Rewarded Color
1
6
Means
Blue Green
44.3 56.1
84.8 89.3
65.7 75.7
Experiment 3. That is, a repeated measurements design analysis of variance again showed significant learning over Trial Blocks ( F = 39.8, d f = 51555, p < .Ol), better learning when green was the rewarded color vs blue ( F = 16.6, df = 1/111, p < .Ol), and n o Prehatch Color Stimulation effect ( F < 1 .O). Thus, the findings from Experiments 3 and 4 failed to show any enhancement effects due t o prehatch color stimulation on posthatch color discrimination learning. Overall, the present findings do not support prehatch color stimulation effects either on posthatch color pecking preferences or on color discrimination learning in a domestic chick. These results affirm and extend Oppenheim’s (1968) failure to find pre- and posthatch color stimulation effects on color pecking preferences of ducklings. Present findings do show an interesting difference in color preferences in the pecking experiments and color discrimination learning experiments. Specifically, when the response was pecking, blue was preferred over green, whereas when green was the rewarded color on the discrimination task, green was associated with superior learning performance, reflecting a greater approach preference for green over blue. This inversion suggests that color preferences in chicks might vary depending upon the type of response system involved. Pecking or feeding type color preferences may differ from such approach preferences as those found in social responsivity or habitat selection. Among studies of color approach (imprinting) preferences in chicks, results of which are quite variable, Schaefer and Hess (1959) suggested a similar possibility. Inconsistent, however, is the finding of a negative preference for green in the only other study of color approach preferences using filtered light, rather than painted objects (Kovach, 1971). Of course, methodological differences from Experiment 4 did exist, e.g., Kovach’s use of intermittent light stimuli vs the present use of cold stress.
Notes ‘At the 450-nm prehatch stimulation wavelength, for example, transmittance of the inner egg membrane and transparent tape, determined using a Beckman Model DU Spectrophotometer, was 60%. Due to changing posture of the embryo in the shell, the eyes were probably not directly exposed to light for much of the time between 15 and 20 days of incubation. Experiment 3 is a portion of an M.S. thesis by the 2nd author (Washington State University, 1974). Acknowledgement is due George A. Leary, Consultant in Optics, for his generous and patient direction of optical procedures and measurements. The authors also wish to thank Justin Wilks, who
COLOR STIMULATION AND PREFERENCES
53 1
assisted with Experiment 4, and Jim Apland, Dennis Boyle, and John Salisbury, who collected the data for Experiment 4. Jim Apland also assisted with computer analyses of the data. Request reprints from: Dr. Gloria J. Fischer, Department of Psychology, Washington State University, Pullman, Washington 99163, U.S.A.
References Dimond, S . J., and Adam, J. H. (1972). Approach behaviour and embryonic visual experience in chicks: Studies of the effects of rate of visual flicker. Anim. Behav., 20: 413-420. Fischer, G. J. (1974). Embryonic sound stimulation and post hatch approach and following by chicks (Gallus domesticus). Paper presented at the meeting of the Psychonomic Society, Boston, Massachusetts, U.S.A. Fischer, G. J., Morris, G. L., and Ruhsam, J. (1975). Color pecking preferences in dark hatched White Leghorn chicks. J. Comp. Physiol. Psychot, 88: 402-406. Kovach, J. K. (1970). Critical period or optimal arousal? Early approach behavior as a function of stimulus age and breed variables in chicks. Dev. Psychol., 3: 73-71. Kovach, J. K. (1971). Effectiveness of different colors in the elicitation and development of approach behavior in chicks. Behaviour, 38: 154-168. Oppenheim, R. W. (1968). Color preferences in the pecking response of newly hatched ducks (Anas platyrhynchos). J. Comp. Physiol. Psychol., 66: 1-17. Paulson, G. W. (1965). Maturation of the evoked response in the duckling. Exp. Neurol., 11: 324-333. Schaefer, H. H., and Hess, E. H. (1959). Color preferences in imprinting objects. 2. Tierpsychol., 16: 161-172.
Four experiments assessed the effects of stimulating chick embryos with colored light at 2 intensity levels. Both posthatch color pecking preferences (Experiments 1 and 2) and color discrimination learning (Experiments 3 and 4)were unaffected. These results affirm and extend a prior finding of no pre- and posthatch colored light stimulation effect on posthatch color preferences in ducklings. The color pecking preferences found replicated prior findings with chicks. However, they djffered from the approach color preferences observed in color discrimination learning.
Visually evoked responses of duck embryos and hatchlings recorded electrophysiologically are modified by prior exposure to light (Paulson, 1965). However, little evidence exists that prehatch light stimulation affects posthatch perception. For example, chicks from eggs exposed to one of several rates of visual flicker on Day 19 of incubation showed no enhanced posthatch responsiveness to that rate. Unexpectedly, chicks exposed to relatively rapid flicker rates (i.e., 1.2 or 3.5 fps) showed enhanced responsiveness to the rate they had not been exposed to (Dimond & Adam, 1972). Oppenheim (1968), on the other hand, found no effects whatsoever from direct stimulation of duck embryos with white or yellow light for 30 hr prior to hatching and for another 20 hr after hatching. These ducklings appeared to be less fearful than dark-hatched ducklings, but their magnitude of pecking and color pecking preferences were unaffected. Because ducklings have a very pronounced and nearly exclusive preference for green, modification of their color preferences might be especially difficult. Chick color preferences, on the other hand, are much less pronounced (e.g., Fischer, Morris, & Ruhsam, 1975) and, thus, seemed more amenable to possible modification. However, the present studies showed that, similar to the manipulation of ducklings, prehatch colored light stimulation failed to affect the magnitude of pecking preferences or color discrimination learning in the White Leghorn chick. Received for publication 4 December 1974 Revised for publication 7 February 1975 Developmental Psychobiology, 8(6): 525-531 (1975) 0 1975 by John Wiley & Sons, Inc.
525
526
FISCHER, DAVIS, AND NORD
Experiments 1 and 2: Prehatch Color Stimulation and Posthatch Color Pecking Preferences Method
Subjects A total of 181 1-day-old White Leghorn chicks (Gallus domesticus), hatched from 16 weekly hatchings, were used in Experiment 1.
Apparatus Prehatch Light Stimulation. The top of a forced-air incubator was replaced with a combination filter, diffusion grid, and light-source enclosure. The color filters (30.5 x 30.5 cm) were compound filters with peak wavelengths of 450 nm (blue), 545 nm (green), and 650 nm (red), and were nonoverlapping, i.e., had half bandwidths of 40 nm, 45 nm, and 45 nm, respectively. The light sources were incandescent bulbs; light intensity could be varied with a rheostat. The intensity at the egg (33 cm below the filter) was measured with a Macbeth illuminometer. The calculated intensity reaching the embryo (accounting for absorption by the transparent tape window and inner egg membrane) was .0518 cd/cm2. For a control (no prehatch light stimulation) condition a filter was not used, but, because the compound filters transmitted infrared, an infrared source (a 350-ohm ceramic resistor) was mounted in the light sockets with the rheostat adjusted to full intensity. Timers regulated the daily light cycle from 0600 hours to 1800 hours with a 3-per-see flickering light (see Kovach, 1970) “on” for 90 sec and “off’ for 180 sec. This on-off sequence totaled 4 hr of light per day. Color Pecking Preferences. The color pecking preference test apparatus and optical calibration have been described by Fischer et al. (1975). Briefly, it consisted of 4 chambers each with a pecking key, filter holder, light source, and counter. A key peck of 5/g pressure activated a microswitch connected to a counter. The light source was a Bausch and Lomb 100-W, variable iris, microscope illuminator. A Photovolt Corporation monochromatic filter could be mounted between each key and its light source. The blue (437 nm), green (541 nm), and red (653 nm) interference filters used for testing pecking preferences were selected to correspond as closely as possible with the peak wavelengths of the filters used for stimulating embryos. An orange (594 nm) filter also was used in testing pecking preferences. Half bandwidths determined with a Beckman Spectrophotometer were 11.5 nm (blue), 8.5 nm (green), 9.0 nm (orange), and 12.5 nm (red). The test chambers were located in a darkened room. Thus, when the illuminators were on, only a .3-cm spot on each key was visible. An arbitrarily selected key, filter (594 nm), and projector were the designated standard. The intensity of the orange target in this standard projector was adjusted, using the projector iris, to .00056 cd/cm2, as measured with a Macbeth illuminometer, 35.6 cm from the key’s surface, This standard intensity was then used to calibrate a Photovolt Corporation 520M Photometer (whch gives an essentially flat response to the radiant energy of the wavelengths used in the present study). The photometer was used, in turn, t o equilibrate the radiance of the 4 different key/light-source combinations. During calibration the photometer was frequently recalibrated against the standard optical system.
COLOR STIMULATION AND PREFERENCES
527
Procedure Incubation, Light Stimulation, and Hatching. Weekly hatches of fertile eggs were set in a commercial incubator for 14 days; then a I-cm square was cut out of each egg shell toward the air sac end (approximating the head position of the embryo). Cutting these holes required removing a piece of shell and the underlying shell membrane without damaging the inner membrane. The holes were covered with transparent tape, and the eggs placed on the top tray of the light stimulation incubator. The holes faced upward toward the light enclosure and source. Timers were activated so that the light stimulation schedule began at 0600 hours on the 15th day of incubation and continued through 1800 hours on the 20th day. The stimulation consisted of flickering (3 fps) red, green, or blue light or infrared (i.e., no light control). At the completion of the stimulation cycle on the 20th day (i.e., after 1800 hours) the eggs were hatched in darkness. Color Pecking Preference Tests. The chicks were tested in sets of 4 when their average age was 24 hr with an age range < 4 hr. They were placed randomly in the 4 test cubicles, facing the pecking key, and 5 min later the light sources were turned on for the 1st of four 15-min pecking sessions. During 5-min intersession intervals, the number of pecks were recorded, and the illuminator iris setting and color filter behind each key were changed. This was done with a board placed over all 4 chambers so that the subject would be in darkness. Thus, the only light source visible to the chicks at any time prior to or during testing was the color spot on the pecking key. Each chick was exposed to all 4 filters colors (blue, green, orange, and red) in a random order over the 4 pecking sessions.
Results and Discussion Seventeen (9%) of the 181 subjects tested did not peck at any filter color over the 4 test sessions and were discarded. For the remaining 164 the mean number of pecks per filter color in each of the prehatch light stimulation conditions was analyzed using a 4 x 4 (Prehatch Color x Posthatch Test Color) repeated measurements design analysis of variance. Results revealed no Prehatch Color effect on either the magnitude of pecking or on color pecking preferences (F’s< 1.0 for Prehatch Color and its interaction with Posthatch Test Color). Overall differences in color preferences did exist (F = 4.8 1, df= 3/48; p < .01; see Fig. 1). Individual F tests revealed that blue was preferred over green and red ([blue vs red]) F = 4.1 1, df = 1/41, p < .05). Orange was preferred over green ( F = 6.83, p < .Ol), but was not quite significantly preferred over red ( F = 3.52, 1.0 > p > .05). Taken together, blue and orange clearly were preferred over green and red, also taken together ( F = 10.8, p < .Ol). These preferences are in complete agreement with color preferences of dark-hatched clucks reported in Fischer et al. (1975). The intensity of prehatch light stimulation in Experiment 1 could have been insufficient to produce posthatch effects on color preferences. Therefore, experiment 1 was replicated on another 120 subjects in Experiment 2 with a 3-fold increase in the intensity of the prehatch light stimulation and twice the total daily amount. Specifically, the intensity of prehatch illumination calculated as in Experiment 1 with the blue filter was increased from the -0518 cd/cm2 in Experiment 1 to .I555 cd/cm’. The duration of prehatch light stimulation was doubled by reversing the 1.5-min on:3-min off ratio in Experiment 1 to a 3-min on: 1.5-min off ratio. Th~sreversal increased the total amount of light stimulation per day from 4 hr to 8 hr. Results again showed no significant effect due
528
FISCHER, DAVIS, AND NORD
Prenotch Treatment &--.A
Red ( 6 5 0 n m )
o----O Green ( 5 4 5 n m ) &--+ Blue ( 4 5 0 n m ) S--* No Light
541
594
653
Wavelength in Nanometers
Fig. 1. The mean number of pecks per filter color by chicks in prehatch color and no-light stimulation groups.
to Prehatch Color stimulation (F’s < 1.0 for Prehatch Color and its interaction with Posthatch Test Color), but again color preferences differed significantly (F = 10.4, df = 3/35, p < .Ol). Specifically, the differences found in Experiment 1 (see Fig. 1 ) were replicated and, in fact, accentuated. These accentuated differences in color preferences may have been due to an increase in the absolute amount of pecking, especially in prehatch light groups. If the absolute amount of pecking were related, in turn, to the increased intensity of prenatal light used in Experiment 2, the effects of prehatch sensory stimulation (see also Fischer, 1974) would appear t o be nonspecific rather than specific. Based on results of Experiments 1 and 2, we conclude that the prehatch intensities and wavelengths used did not affect embryos such that their posthatch color preferences were changed. A discrimination task, however, might be a more sensitive measure of prehatch color stimulation effects. This possibility was tested in Experiments 3 and 4. Experiment 3 compared blue, green, white, and no prehatch light stimulation groups on posthatch learning of a blue.green light discrimination in a Y-maze. The inclusion of a white-light control group was to insure that possible enhancement effects of prehatch color stiniulation on color discrimination learning could be attributed t o hue, as opposed to light stimulation, per se.
Experiments 3 and 4: Prehatch Color Stimulation and Posthatch Color Discrimination Learning Method The selection of subjects in Experiment 3 (143 White Leghorn chcks hatched from 12 weekly settings), and the apparatus and procedure for prehatch light stimulation followed that of Experiment 1 with one exception: the additoin of a white-light control (incandescent bulbs only) group.
COLOR STIMULATION AND PREFERENCES
529
Color discrimination training was conducted in a Y-maze in a 10°C temperaturecontrolled cold room. The Y-maze had optical and heat systems at the end of each alley. Each optical system consisted of a microscope illuminator (those used in Experiments 1 and 2), color filter, and 2 mirrors to project a 2.54-cm square of color onto the goal box end wall. Filters were mounted in movable holders and had peak wavelengths of 437 nm (blue) and 541 nm (green) with half bandwidths of 11.5 nm and 8.5 nm. respectively. The intensity of the projected colors was equilibrated (using the same procedure and instruments as with the pecking apparatus) at .0085 cd/cm2. Each heat system consisted of a 250-W heat lamp and an infrared filter that transmitted no visible light into the maze. Both heat lamps could be activated simultaneously by a 20-sec timer. Six pairs of chicks, closely matched for age, were tested weekly. Half, randomly selected, learned the blue-green discrimination with blue positive, and the other half had green positive. In this manner 18 subjects were run in each of the 8 combinations of rewarded color (blue or green) and prehatch light stimulation condition (blue, green, white, or none). Each pair of chicks was run in tandem on the blue-green task; each received 6 blocks of correction trials: 7 trials onBlocks 1-3at average pair ages of 22,24, and 26 hr, and 9 trials per block on Blocks 3-6 at ages 44,46, and 48 hr. Entrance into (or, on correction trials, prodding into) the correct end box activated the timer for 20 sec of heat reward. During a 3-min intertrial interval, each chick was returned to a holding box while the other was tested. The position of the correct goal box was varied randomly for each pair. Between blocks of trials, subjects were kept in a darkened 29°C room. Thus, posthatch light experience was restricted to the blue and green light visible during learning trials.
Results and Discussion The number of correct choices per chick per trial block was converted to a percent correct score whch showed heterogeneity among between-group variances (xz = 31 3,df = 7, p < .Ol). An arcsin J p transformation of initial (Block 1) and terminal (Block 6) percentages reduced this heterogeneity to an acceptable level (x' = 113,df= 7, p < .12). These transformed data were analyzed using a 4 x 2 x 2 (Prehatch Light Stimulation groups [blue, green, white, or none] x Positive Stimulus Color [blue or green] x Trial Block [l and 61) repeated measurements design analysis of variance. Results showed 2 significant effects (see Table 1): increased learning over trials ( F = 424.4, df = 1/135, p < .Ol), and better learning when the positive color was green than when it was blue (F = 14.1, df = 1/135, p < .Ol). The latter difference (see rewarded color means in Table 1) was clearly related to an approach preference for green over blue, in that the chicks chose green over blue rather consistently, even on early trial blocks. The Prehatch Light Stimulation effect approached significance (F = 2.46, df = 3/135, p < .06), but the trend reflected a somewhat negative effect on learning from prehatch white stimulation rather than any enhancement effect from prehatch color stimulation. For example, overall mean percent correct responses for prehatch no-light, blue, green, and white light groups were 71.7, 70.3, 73.9, and 66.7, respectively. As in Experiment 1, the failure in Experiment 3 to show a Prehatch Color Stimulation effect could have been due to insufficient light intensity. Thus, another 117 chicks received prehatch blue, green, or no light at the higher (.1555 cd/cm2) intensity used in Experiment 2. Results from Experiment 4 were quite similar to those of
530
FISCHER, DAVIS, AND NORD
TABLE. I . Mean Percent Correct Responses on First (1)and Last ( 6 ) Trial Blocks on a Blue-Green Discrimination us a Function of the Rewarded Color. Trial Block Rewarded Color
1
6
Means
Blue Green
44.3 56.1
84.8 89.3
65.7 75.7
Experiment 3. That is, a repeated measurements design analysis of variance again showed significant learning over Trial Blocks ( F = 39.8, d f = 51555, p < .Ol), better learning when green was the rewarded color vs blue ( F = 16.6, df = 1/111, p < .Ol), and n o Prehatch Color Stimulation effect ( F < 1 .O). Thus, the findings from Experiments 3 and 4 failed to show any enhancement effects due t o prehatch color stimulation on posthatch color discrimination learning. Overall, the present findings do not support prehatch color stimulation effects either on posthatch color pecking preferences or on color discrimination learning in a domestic chick. These results affirm and extend Oppenheim’s (1968) failure to find pre- and posthatch color stimulation effects on color pecking preferences of ducklings. Present findings do show an interesting difference in color preferences in the pecking experiments and color discrimination learning experiments. Specifically, when the response was pecking, blue was preferred over green, whereas when green was the rewarded color on the discrimination task, green was associated with superior learning performance, reflecting a greater approach preference for green over blue. This inversion suggests that color preferences in chicks might vary depending upon the type of response system involved. Pecking or feeding type color preferences may differ from such approach preferences as those found in social responsivity or habitat selection. Among studies of color approach (imprinting) preferences in chicks, results of which are quite variable, Schaefer and Hess (1959) suggested a similar possibility. Inconsistent, however, is the finding of a negative preference for green in the only other study of color approach preferences using filtered light, rather than painted objects (Kovach, 1971). Of course, methodological differences from Experiment 4 did exist, e.g., Kovach’s use of intermittent light stimuli vs the present use of cold stress.
Notes ‘At the 450-nm prehatch stimulation wavelength, for example, transmittance of the inner egg membrane and transparent tape, determined using a Beckman Model DU Spectrophotometer, was 60%. Due to changing posture of the embryo in the shell, the eyes were probably not directly exposed to light for much of the time between 15 and 20 days of incubation. Experiment 3 is a portion of an M.S. thesis by the 2nd author (Washington State University, 1974). Acknowledgement is due George A. Leary, Consultant in Optics, for his generous and patient direction of optical procedures and measurements. The authors also wish to thank Justin Wilks, who
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assisted with Experiment 4, and Jim Apland, Dennis Boyle, and John Salisbury, who collected the data for Experiment 4. Jim Apland also assisted with computer analyses of the data. Request reprints from: Dr. Gloria J. Fischer, Department of Psychology, Washington State University, Pullman, Washington 99163, U.S.A.
References Dimond, S . J., and Adam, J. H. (1972). Approach behaviour and embryonic visual experience in chicks: Studies of the effects of rate of visual flicker. Anim. Behav., 20: 413-420. Fischer, G. J. (1974). Embryonic sound stimulation and post hatch approach and following by chicks (Gallus domesticus). Paper presented at the meeting of the Psychonomic Society, Boston, Massachusetts, U.S.A. Fischer, G. J., Morris, G. L., and Ruhsam, J. (1975). Color pecking preferences in dark hatched White Leghorn chicks. J. Comp. Physiol. Psychot, 88: 402-406. Kovach, J. K. (1970). Critical period or optimal arousal? Early approach behavior as a function of stimulus age and breed variables in chicks. Dev. Psychol., 3: 73-71. Kovach, J. K. (1971). Effectiveness of different colors in the elicitation and development of approach behavior in chicks. Behaviour, 38: 154-168. Oppenheim, R. W. (1968). Color preferences in the pecking response of newly hatched ducks (Anas platyrhynchos). J. Comp. Physiol. Psychol., 66: 1-17. Paulson, G. W. (1965). Maturation of the evoked response in the duckling. Exp. Neurol., 11: 324-333. Schaefer, H. H., and Hess, E. H. (1959). Color preferences in imprinting objects. 2. Tierpsychol., 16: 161-172.
