The Journal of General Psychology
ISSN: 0022-1309 (Print) 1940-0888 (Online) Journal homepage: http://www.tandfonline.com/loi/vgen20
Visual Pathways, Acuity Dominance, and Visual Half-Field Asymmetry Ray Parker , Paul Satz & E. P. Horne To cite this article: Ray Parker , Paul Satz & E. P. Horne (1976) Visual Pathways, Acuity Dominance, and Visual Half-Field Asymmetry, The Journal of General Psychology, 95:2, 233-240, DOI: 10.1080/00221309.1976.9711346 To link to this article: http://dx.doi.org/10.1080/00221309.1976.9711346
Published online: 06 Jul 2010.
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Date: 12 November 2015, At: 13:25
The Journal of General Psychology, 1976, 95, 233-240
VISUAL PATHWAYS, ACUITY DOMINANCE, AND VISUAL HALF-FIELD ASYMMETRY* Modigan Army Medical Center, Tacoma, Washington; and Department of Psychology, University of Florida, Gaincsville
Downloaded by [University of Birmingham] at 13:25 12 November 2015
RAY PARKER,'PAULSATZ,AND E. P. HORNE
SUMMARY The effects of the visual pathways and acuity dominance on visual halffield (VHF) recall of verbal stimuli were investigated with 36 right-handed male undergraduates, with the use of the Hines-Satz short-term memory paradigm under monocular conditions. Scores for stimuli transmitted via the left temporal and right nasal pathways were significantly greater than those for stimuli transmitted via the left nasal and right temporal pathways. No other significant differences were found for either the pathways or acuity dominance variables. The results were hypothesized to reflect the primary influence of hemispheric asymmetry of function on the VHF recall task.
INTRODUCTION Visual half-field (VHF) research is making a significant contribution to the growing body of empirical knowledge on hemispheric asymmetry of function A.
(5, 6, 7, 12, 13, 14). The purpose of the present study is to determine the way VHF stimulus report is affected by both the visual pathways and acuity dominanci?. VHF perception certainly involves the transmission of stimulus signals over each of the four neuroanatomical pathways in the visual system. Any difference in signal transmission efficiency among the visual pathways would be expected to affect VHF asymmetry. Thus, information concerning the transmission efficiency of each pathway would provide data on their contribution to VHF asymmetry and possibly aid in suggesting an explanation of this asymmetry.
* Received in the Editorial Office, Provincetown, Massachusetts, on July 2 , 1975. Copyright, 1376. by The Journal Press. ' The senior author completed this research at the University of Florida as partial fulhllment for the requirements of the Doctor of Philosophydegree. Requests for reprints should be sent to the senior author at the address shown at the end of this article. 233
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Initial studies with threshold-recognition paradigms attempted to provide information on this pathway variable (1,3, 8, 15, 16). However, inconsistent and conflicting findings made the inferential utility of these studies limited, Explanations of this lack of agreement between studies involved variations in research methodology, especially the absence of specific procedures to control S fixation. Using improved methodology, however, other investigators have successfully studied the pathways variable with threshold-recognition designs. Using a procedure to control fixation and threshold-exposure durations, McKeever and Huling (13) found that verbal stimuli transmitted over the left temporal and right nasal pathways exhibited no significant differences in stimulus recognition but were recognized significantly better than stimuli transmitted over the left nasal and right temporal pathways. In addition, no significant difference for stimulus recognition was found between these latter two pathways. The right VHF effect was greater, however, for the left eye than for the right eye. Also employing controlled-fixation methodology, McKeever and Huling (14) presented bilateral arrays of words at threshold durations and found that recognition scores for the left temporal and right nasal pathways were significantly superior to those for the left nasal and right temporal pathways. Thus, the effects of the pathway variable are reported for the threshold recognition VHF paradigm. The present research, however, is designed specifically to investigate differences in stimulus report for the four visual pathways within the context of a short-term memory (STM) design. VHF perception may also be affected by acuity dominance. The task of apprehension of stimuli in the visual fields clearly requires adequate visual acuity for both monocular and binocular viewing conditions. Kahneman (10) defines visual acuity as the ability to resolve details of form. Acuity may be operationally defined as the minimal size of detail that can still be resolved. Under monocular conditions, if one eye is capable of resolving smaller and more detailed stimuli than the other, then one may predict that this more acute eye might yield a superior performance under the conditions of rapid stimulus identification and processing imposed by a VHF task. Thus, the relationship between acuity dominance and VHF asymmetry might be studied in terms of VHF recall scores obtained under monocular conditions. Some studies relating acuity dominance to VHF asymmetry have done so in the absence of any objective assessment of acuity dominance. The latter variable has simply been used to interpret obtained results (1, 8, 15, 17). Hayashi and Bryden (4), however, did assess acuity dominance by means of
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a standard Sloan chart in their study of VHF asymmetry. Using thresholdexposure durations, these researchers found that right-handed right acuitydominant Ss exhibited a right VHF superiority for recognition of verbal stimuli. On the other hand, right-handed left acuity-dominant Ss exhibited no differences in recognition in the VHFs. Although assessing acuity dominance in a controlled manner, Hayashi and Bryden nevertheless failed to use a design that would assure the maintenance of fixation. Also, no monocular viewing conditions were included in their procedure. With earlier methodological inadequacies as cited, the possibility exists that acuity dominance may influence VHF asymmetry in a threshold recognition paradigm. The present study, therefore, proposes to vary acuity dominance under monocular viewing conditions in order to provide information on the role of this variable in a VHF STM paradigm. B. METHOD 1. Equipment
The Armed Forces Vision Tester (11) consists of a sheet metal housing containing a viewing box and lens system. The test plates are held by two revolving drums. Each drum is illuminated by a tubular light bulb inside the drum (9) Test plate 9 for near visual acuity consists of letter stimuli of various sizes. Twenty different letters of equal size corresponding to a given acuity level (ZO/SO, 20/40, 20/30, 20/25, 20/20, 20/17, ZO/lS, and 20/12) compose each row on the plate. Each acuity level is represented by two such rows. The VHF equipment consists of a long table with a commercial chin rest mounted at one end and a large rear view projection screen (4'10" away from the chin rest) mounted at the other end. Also included is a Kodak Analyst 16 mm projector with modified governor and a stimulus film which is described as follows: Sixty-six trials compose the film. Each of these trials consists of a central fixmon indicator (cross) and five pairs of single block letters appearing white against the darker background of the screen. The cross appears for approximately one itnd one-half seconds, followed in succession by the five letter-pairs, consisting of one letter at fixation and one in a VHF. Each letter pair appears for 330 msec with no interpair interval. Within each trial, all letters are exposed in the same VHF. Over trials, letters are presented at fixation and alternately to each VHF. No letter appears more than once on any given trial. The interval between trials is 15 seconds. Each letter subtends approximately one degree of visual arc in height and 45 minutes in width. Approximately three degrees of visual arc exist between the center of fixation and the inner edge of the VHF letters.
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2.
Procedure
The S was placed in a dark room containing the equipment. Handedness was verified by the S’s self-report. The S was seated in front of the Armed Forces Vision Tester. Illumination at the plate surface was 18.23 foot lamberts as measured with the MacBeth Illuminometer. The E collected acuity data for each of the S’s eyes. With the right eye occluded, the S was instructed to view the stimulus display (with the left eye) and identify as many letters as possible at each of the eight acuity levels. For a given acuity level viewed by any one eye, 20 letters were present for identification, since the S viewed the first 10 letters (left half of the plate) of a row with the left eye and the last 10 (right half of the plate) with the right eye. Guessing was encouraged and all Ss were required to report all perceived letters. Letters incorrectly identified at each level were marked on the data sheet. The same procedure was then repeated for the right eye. Ss who wore corrective lenses were instructed not to remove them. Also, Ss were questioned regarding the presence of any visual abnormalities that might have precluded participation in this study (cataracts, visual field defects, etc.). After acuity data were obtained, the S was seated at the long table with his head positioned in the chin rest. One eye was then occluded by means of an adhesive eye patch. In order to control for practice effects between eyes, half of the Ss viewed the stimulus film first with the left eye, then with the right, and the other half viewed the film in the reverse order. At the beginning of a session, the S was instructed to fixate on the central cross and then on the five successive letters presented at fixation. He was further instructed to report allfive letters presented at fixation before reporting any letters presented to the left or right VHFs. He was permitted, however, to report the letters from the fixation or VHF groups in any order. All responses were recorded. Six practice trials and 60 test trials were administered for each of two viewing sessions, one for each of an S’s eyes. A period of interpolated tasks (finger tapping, manual dexterity tasks), given under normal illumination conditions and lasting approximately 20 minutes, temporally separated the two viewing sessions. 3.
Scoring
With the monocular acuity data, acuity dominance for each S was determined by the following method. An acuity threshold was determined for each eye. It was obtained by recording the number of letters correctly identified at all levels of acuity from the less superior (2O/SO) to the more
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et al.
23 7
superior t20/12). Then, the level of acuity was determined at which an S (a) identified 5 0 percent or more letters (10 or more) at that level but (6) failed to reach 50 percent correct identifications for any of the more superior levels. Thus, for Ss who obtained acuity thresholds on different levels, the eye with a threshold at a better level was labeled the dominant eye (this does not refer to ocular dominance). On the other hand, for Ss whose eyes reached acuity threshold on the same level, the eye having the greater number of correct identifications at that level was labeled the dominant eye. Thus, two acuity dominance groups (right dominant and left dominant) were obtained. With respect to VHF recall scores, the scoring procedure was as follows. A trial was not scored unless the S correctly reported all five letters at fixation. Thus, the possibility existed of obtaining spurious differences in VHF recall scores as a function of the number of trials on which such scores were based. Since such differences would have been confounded with any differences presumably mediated by hemispheric asymmetry factors, operation of the former variable was controlled by the use of adjusted recall scores (ARSs). These scores were derived on the basis of the S’s VHF recall scores for each of five serial positions associated with a particular VHF viewed by a particular eye. Thus, each of the five serial position scores for a certain VHF by eye viewing condition was divided by the number of trials scored for that viewing condition. As a result, 2 0 ARSs were obtained for each S, one ARS for each serial position by VHF by eye condition.
Subjects All Ss were male undergraduates at the University of Florida who were right-handed as determined by self-report, and their ages ranged from 18 to 25. The original pool of 58 Ss was reduced to the 3 6 used in this study by the following selection procedure: All Ss reporting any family history of lefthandedness were separated; the remaining sample was divided into groups on the basis of order-of-viewing (Order I and Order II) and acuity dominance (right or left). Nine Ss were randomly selected from each of the four order-acuity dominance groups to compose the sample of 36. 4.
C. RESULTS The analysis of variance shows two significant main effects: VHF and serial position. In addition, the interaction between them is significant. The VHF effect (F = 50.35, p < .Or)indicates that mean recall scores for stimuli transmitted over the left temporal and right nasal pathways (right VHF) were significantly superior to mean recall scores for those transmitted over
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the left nasal and right temporal pathways (left VHF). The serial position effect (F = 128.57, p < .01) indicates that mean recall scores differed significantly as a function of serial position. The VHF by serial position interaction (F = 3.71, p < .Ol),together with the t tests shown in Table 1, indicates that a significant right VHF superiority for mean recall scores was obtained for serial positions 1 through 4 but not for 5. Additionally, the magnitude of recall was greatest for the last serial position (14) in both VHFs. The latter findings on the serial position variable essentially replicate those reported in previous research ( 6 ) . Nonsignificant main effects were order of viewing (F = 1.25), acuity dominance (F = .03), and eye (F = .03). Interaction effects other than VHF by serial position were also nonsignificant. The eye by VHF interaction (F = .01) indicates that mean recall scores for stimuli transmitted over the left temporal and right nasal pathways did not differ significantly (see Table 2). Also, the absence of interaction shows that mean recall scores for stimuli transmitted over the left nasal and right temporal pathways were not significantly different. In addition, the difference between mean recall scores for stimuli transmitted over the left temporal and left nasal pathways was not significantly greater than the difference between mean recall scores for stimuli transmitted over the right nasal and right temporal pathways. The
1
TABLE 1 TESTSBETWEENVISUALHALF-FIELD (VHF) ADJUSTED RECALLSCORE MEANSFOR EACHSERIALPOSITION Serial position
Condition Right VHF Left VHF t
* p < .01; df ** p < .02; df
1
2
3
4
5
.232 ,164 4.297*
.235 ,156 4.91 1*
.229 ,172 3.069*
.2a7 ,240 2.45**
,619 ,622 ,613
= 160. = 160.
TABLE 2 ADJUSTEDRECALLSCOREMEANSFOR THE EYE BY VISUALHALF-FIELD (VHF) VIEWINGCONDITIONS WITH THE CORRESPONDING VISUALPATHWAYS Condition Right VHF Left VHF
Left eye Left temporal
Right eye Right nasal
,320
,322
Left nasal
Right temporal
.270
.272
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failure of acuity dominance to reach significance is indicative of a minimal relationship between this variable and performance on the VHF STM task.
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D. DISCUSSION The transmission of discrete, lettered stimuli has provided results which are generally consistent with present concepts of the human visual system and current theories concerning hemispheric asymmetry of function (2, 6, 13, 14). With respect to intereye variability in magnitude of right VHF superiority, the obtained results do not agree with those of McKeever and Huling (13). Such variation in results obtained with the Hines-Satz and McKeever paradigms is not surprising, since correct responding in the latter design depends very heavily on the S’s ability to recognize single stimuli presented at threshold durations. The Hines-Satz paradigm, on the other hand, employs exposure durations well above threshold and includes several stimuli on each trial. For this reason, successful report of stimuli with this latter paradigm may be primarily dependent on the S’s processing and short-term storage abilities. In this context, perceptual recognition factors may actually play a very minimal role in multiple-stimulus long-duration procedures, such as the Hines-Satz paradigm. When this hypothesis is considered together with the nonsignificant effects of acuity dominance, an explanation can be suggested for both the acuity dominance results and the absence of intereye differences in VHF asymmetry. Perhaps perceptual factors involving intereye differences in perceptual ability are more important at threshold exposure durations and do not operate with any significance in some paradigms using more lengthy presentation times. Acuity dominance might certainly be related to VHF asymmetry in this way and, on this basis, one would not expect it to influence the asymmetry to any significant extent in the Hines-Satz paradigm. However, VHF asymmetry in threshold recognition designs might be affected significantly by intra-S differences in acuity dominance. Hemispheric asymmetry of function and acuity dominance could theoretically interact in such a design to produce various intereye recall differences. Only research investigating the effects of acuity dominance at threshold durations would provide additional information.
REFERENCES 1.
BARTON, M.,GOODGLASS,H.,81 SHN, A. Differential recognition of tachistoscopically presented English and Hebrew words in right and left visual half-fields. Percept. & Motor Skilk, 1965, 41, 431-437.
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BRINDLEY,G. Physiology of the Retina and Visual Pathway. Baltimore: Williams & Wilkins, 1970. 3. CROVITZ, H., & DAVES,W. Tendencies to eye movement and perceptual accuracy. J. Erper. Psychol., 1962, 63, 495-498. T., & BRYDEN,M. Ocular dominance and perceptual asymmetry. Percept. 6 4. HAYASHI, Motor Skills, 1967, 25, 605-612. 5. HINES,D., & SATZ,P. Superiority of the right visual half-fields in right-handers for recall of digits presented at varying rates. ,Veuropsychologia, 1971, 9, 2 1-25. 6. HINES, D., SATZ,P., & CLEMENTINO, T. Perceptual and memory components of the superior recall of letters from the right visual half-fields. Neuropsychologia, 1973, 11,
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2.
175-180.
7.
HINES,D., SATZ,P., SCHELL,B., & SCHMIDLIN, S. Differential recall of digits in the left and right visual half-fields under free and fixed order of recall. Neuropsychobgia, 1969, 7, 13-22.
HIRATA,K-I., & OSAKA,R.Tachistoscopic recognition of Japanese materials in left and right visual fields. Psychologia, 1967, 10, 7-18. 9. HORNE,E. P., & HINES,D. Changes in visual acuity in repeated measurement. J . G e m Psychol., 1969, 80, 93-97. D. Method, findings and theory in studies of visual masking. Psychol. Bull., 10. KAHNEMAN, 8.
1968, 70, 404-425. 11. 12. 13. 14. 1s.
16. 17.
Manual of Instruction, Armed Forces Vision Tester. Ann Arbor, Michigan: Armed Forces-National Research Council Vision Committee Secretariat, 195 7. MCKEEVER, W., & GILL,K. Visual half-field differences in masking effects for sequential letter stimuli in the right and left-handed. Neuropsychologia, 1972, 10, 111-117. MCKEEVER, W., & HULING,M. Left-cerebral hemisphere superiority in tachistoscopic word-recognition performances. Percept. G Motor Skills, 1970, 30, 763-766. -. Lateral dominance in tachistoscopic word recognition performances obtained with simultaneous bilateral input. Neuropsychologia, 197 1, 9, 15-20. OVERTON,W., & WEINER,M. Visual field position and word recognition thresholds. 1. Erper. Psychol., 1966, 71, 249-253. SCHELL,J. Ocular dominance and visual hemifield differences. Master’s thesis, University of Florida, Gainesville, 1968. WYKE,M., & ETTLINCER, G . Efficiency of recognition in right and left visual fields. Arch. Neurol., 1961, 5, 95-101.
Madigan Army Medical Center P.O. Box 55 Tacoma, Washington 98431
ISSN: 0022-1309 (Print) 1940-0888 (Online) Journal homepage: http://www.tandfonline.com/loi/vgen20
Visual Pathways, Acuity Dominance, and Visual Half-Field Asymmetry Ray Parker , Paul Satz & E. P. Horne To cite this article: Ray Parker , Paul Satz & E. P. Horne (1976) Visual Pathways, Acuity Dominance, and Visual Half-Field Asymmetry, The Journal of General Psychology, 95:2, 233-240, DOI: 10.1080/00221309.1976.9711346 To link to this article: http://dx.doi.org/10.1080/00221309.1976.9711346
Published online: 06 Jul 2010.
Submit your article to this journal
Article views: 5
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=vgen20 Download by: [University of Birmingham]
Date: 12 November 2015, At: 13:25
The Journal of General Psychology, 1976, 95, 233-240
VISUAL PATHWAYS, ACUITY DOMINANCE, AND VISUAL HALF-FIELD ASYMMETRY* Modigan Army Medical Center, Tacoma, Washington; and Department of Psychology, University of Florida, Gaincsville
Downloaded by [University of Birmingham] at 13:25 12 November 2015
RAY PARKER,'PAULSATZ,AND E. P. HORNE
SUMMARY The effects of the visual pathways and acuity dominance on visual halffield (VHF) recall of verbal stimuli were investigated with 36 right-handed male undergraduates, with the use of the Hines-Satz short-term memory paradigm under monocular conditions. Scores for stimuli transmitted via the left temporal and right nasal pathways were significantly greater than those for stimuli transmitted via the left nasal and right temporal pathways. No other significant differences were found for either the pathways or acuity dominance variables. The results were hypothesized to reflect the primary influence of hemispheric asymmetry of function on the VHF recall task.
INTRODUCTION Visual half-field (VHF) research is making a significant contribution to the growing body of empirical knowledge on hemispheric asymmetry of function A.
(5, 6, 7, 12, 13, 14). The purpose of the present study is to determine the way VHF stimulus report is affected by both the visual pathways and acuity dominanci?. VHF perception certainly involves the transmission of stimulus signals over each of the four neuroanatomical pathways in the visual system. Any difference in signal transmission efficiency among the visual pathways would be expected to affect VHF asymmetry. Thus, information concerning the transmission efficiency of each pathway would provide data on their contribution to VHF asymmetry and possibly aid in suggesting an explanation of this asymmetry.
* Received in the Editorial Office, Provincetown, Massachusetts, on July 2 , 1975. Copyright, 1376. by The Journal Press. ' The senior author completed this research at the University of Florida as partial fulhllment for the requirements of the Doctor of Philosophydegree. Requests for reprints should be sent to the senior author at the address shown at the end of this article. 233
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Initial studies with threshold-recognition paradigms attempted to provide information on this pathway variable (1,3, 8, 15, 16). However, inconsistent and conflicting findings made the inferential utility of these studies limited, Explanations of this lack of agreement between studies involved variations in research methodology, especially the absence of specific procedures to control S fixation. Using improved methodology, however, other investigators have successfully studied the pathways variable with threshold-recognition designs. Using a procedure to control fixation and threshold-exposure durations, McKeever and Huling (13) found that verbal stimuli transmitted over the left temporal and right nasal pathways exhibited no significant differences in stimulus recognition but were recognized significantly better than stimuli transmitted over the left nasal and right temporal pathways. In addition, no significant difference for stimulus recognition was found between these latter two pathways. The right VHF effect was greater, however, for the left eye than for the right eye. Also employing controlled-fixation methodology, McKeever and Huling (14) presented bilateral arrays of words at threshold durations and found that recognition scores for the left temporal and right nasal pathways were significantly superior to those for the left nasal and right temporal pathways. Thus, the effects of the pathway variable are reported for the threshold recognition VHF paradigm. The present research, however, is designed specifically to investigate differences in stimulus report for the four visual pathways within the context of a short-term memory (STM) design. VHF perception may also be affected by acuity dominance. The task of apprehension of stimuli in the visual fields clearly requires adequate visual acuity for both monocular and binocular viewing conditions. Kahneman (10) defines visual acuity as the ability to resolve details of form. Acuity may be operationally defined as the minimal size of detail that can still be resolved. Under monocular conditions, if one eye is capable of resolving smaller and more detailed stimuli than the other, then one may predict that this more acute eye might yield a superior performance under the conditions of rapid stimulus identification and processing imposed by a VHF task. Thus, the relationship between acuity dominance and VHF asymmetry might be studied in terms of VHF recall scores obtained under monocular conditions. Some studies relating acuity dominance to VHF asymmetry have done so in the absence of any objective assessment of acuity dominance. The latter variable has simply been used to interpret obtained results (1, 8, 15, 17). Hayashi and Bryden (4), however, did assess acuity dominance by means of
Downloaded by [University of Birmingham] at 13:25 12 November 2015
RAY PARKER et al.
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a standard Sloan chart in their study of VHF asymmetry. Using thresholdexposure durations, these researchers found that right-handed right acuitydominant Ss exhibited a right VHF superiority for recognition of verbal stimuli. On the other hand, right-handed left acuity-dominant Ss exhibited no differences in recognition in the VHFs. Although assessing acuity dominance in a controlled manner, Hayashi and Bryden nevertheless failed to use a design that would assure the maintenance of fixation. Also, no monocular viewing conditions were included in their procedure. With earlier methodological inadequacies as cited, the possibility exists that acuity dominance may influence VHF asymmetry in a threshold recognition paradigm. The present study, therefore, proposes to vary acuity dominance under monocular viewing conditions in order to provide information on the role of this variable in a VHF STM paradigm. B. METHOD 1. Equipment
The Armed Forces Vision Tester (11) consists of a sheet metal housing containing a viewing box and lens system. The test plates are held by two revolving drums. Each drum is illuminated by a tubular light bulb inside the drum (9) Test plate 9 for near visual acuity consists of letter stimuli of various sizes. Twenty different letters of equal size corresponding to a given acuity level (ZO/SO, 20/40, 20/30, 20/25, 20/20, 20/17, ZO/lS, and 20/12) compose each row on the plate. Each acuity level is represented by two such rows. The VHF equipment consists of a long table with a commercial chin rest mounted at one end and a large rear view projection screen (4'10" away from the chin rest) mounted at the other end. Also included is a Kodak Analyst 16 mm projector with modified governor and a stimulus film which is described as follows: Sixty-six trials compose the film. Each of these trials consists of a central fixmon indicator (cross) and five pairs of single block letters appearing white against the darker background of the screen. The cross appears for approximately one itnd one-half seconds, followed in succession by the five letter-pairs, consisting of one letter at fixation and one in a VHF. Each letter pair appears for 330 msec with no interpair interval. Within each trial, all letters are exposed in the same VHF. Over trials, letters are presented at fixation and alternately to each VHF. No letter appears more than once on any given trial. The interval between trials is 15 seconds. Each letter subtends approximately one degree of visual arc in height and 45 minutes in width. Approximately three degrees of visual arc exist between the center of fixation and the inner edge of the VHF letters.
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Downloaded by [University of Birmingham] at 13:25 12 November 2015
2.
Procedure
The S was placed in a dark room containing the equipment. Handedness was verified by the S’s self-report. The S was seated in front of the Armed Forces Vision Tester. Illumination at the plate surface was 18.23 foot lamberts as measured with the MacBeth Illuminometer. The E collected acuity data for each of the S’s eyes. With the right eye occluded, the S was instructed to view the stimulus display (with the left eye) and identify as many letters as possible at each of the eight acuity levels. For a given acuity level viewed by any one eye, 20 letters were present for identification, since the S viewed the first 10 letters (left half of the plate) of a row with the left eye and the last 10 (right half of the plate) with the right eye. Guessing was encouraged and all Ss were required to report all perceived letters. Letters incorrectly identified at each level were marked on the data sheet. The same procedure was then repeated for the right eye. Ss who wore corrective lenses were instructed not to remove them. Also, Ss were questioned regarding the presence of any visual abnormalities that might have precluded participation in this study (cataracts, visual field defects, etc.). After acuity data were obtained, the S was seated at the long table with his head positioned in the chin rest. One eye was then occluded by means of an adhesive eye patch. In order to control for practice effects between eyes, half of the Ss viewed the stimulus film first with the left eye, then with the right, and the other half viewed the film in the reverse order. At the beginning of a session, the S was instructed to fixate on the central cross and then on the five successive letters presented at fixation. He was further instructed to report allfive letters presented at fixation before reporting any letters presented to the left or right VHFs. He was permitted, however, to report the letters from the fixation or VHF groups in any order. All responses were recorded. Six practice trials and 60 test trials were administered for each of two viewing sessions, one for each of an S’s eyes. A period of interpolated tasks (finger tapping, manual dexterity tasks), given under normal illumination conditions and lasting approximately 20 minutes, temporally separated the two viewing sessions. 3.
Scoring
With the monocular acuity data, acuity dominance for each S was determined by the following method. An acuity threshold was determined for each eye. It was obtained by recording the number of letters correctly identified at all levels of acuity from the less superior (2O/SO) to the more
Downloaded by [University of Birmingham] at 13:25 12 November 2015
RAY PARKER
et al.
23 7
superior t20/12). Then, the level of acuity was determined at which an S (a) identified 5 0 percent or more letters (10 or more) at that level but (6) failed to reach 50 percent correct identifications for any of the more superior levels. Thus, for Ss who obtained acuity thresholds on different levels, the eye with a threshold at a better level was labeled the dominant eye (this does not refer to ocular dominance). On the other hand, for Ss whose eyes reached acuity threshold on the same level, the eye having the greater number of correct identifications at that level was labeled the dominant eye. Thus, two acuity dominance groups (right dominant and left dominant) were obtained. With respect to VHF recall scores, the scoring procedure was as follows. A trial was not scored unless the S correctly reported all five letters at fixation. Thus, the possibility existed of obtaining spurious differences in VHF recall scores as a function of the number of trials on which such scores were based. Since such differences would have been confounded with any differences presumably mediated by hemispheric asymmetry factors, operation of the former variable was controlled by the use of adjusted recall scores (ARSs). These scores were derived on the basis of the S’s VHF recall scores for each of five serial positions associated with a particular VHF viewed by a particular eye. Thus, each of the five serial position scores for a certain VHF by eye viewing condition was divided by the number of trials scored for that viewing condition. As a result, 2 0 ARSs were obtained for each S, one ARS for each serial position by VHF by eye condition.
Subjects All Ss were male undergraduates at the University of Florida who were right-handed as determined by self-report, and their ages ranged from 18 to 25. The original pool of 58 Ss was reduced to the 3 6 used in this study by the following selection procedure: All Ss reporting any family history of lefthandedness were separated; the remaining sample was divided into groups on the basis of order-of-viewing (Order I and Order II) and acuity dominance (right or left). Nine Ss were randomly selected from each of the four order-acuity dominance groups to compose the sample of 36. 4.
C. RESULTS The analysis of variance shows two significant main effects: VHF and serial position. In addition, the interaction between them is significant. The VHF effect (F = 50.35, p < .Or)indicates that mean recall scores for stimuli transmitted over the left temporal and right nasal pathways (right VHF) were significantly superior to mean recall scores for those transmitted over
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the left nasal and right temporal pathways (left VHF). The serial position effect (F = 128.57, p < .01) indicates that mean recall scores differed significantly as a function of serial position. The VHF by serial position interaction (F = 3.71, p < .Ol),together with the t tests shown in Table 1, indicates that a significant right VHF superiority for mean recall scores was obtained for serial positions 1 through 4 but not for 5. Additionally, the magnitude of recall was greatest for the last serial position (14) in both VHFs. The latter findings on the serial position variable essentially replicate those reported in previous research ( 6 ) . Nonsignificant main effects were order of viewing (F = 1.25), acuity dominance (F = .03), and eye (F = .03). Interaction effects other than VHF by serial position were also nonsignificant. The eye by VHF interaction (F = .01) indicates that mean recall scores for stimuli transmitted over the left temporal and right nasal pathways did not differ significantly (see Table 2). Also, the absence of interaction shows that mean recall scores for stimuli transmitted over the left nasal and right temporal pathways were not significantly different. In addition, the difference between mean recall scores for stimuli transmitted over the left temporal and left nasal pathways was not significantly greater than the difference between mean recall scores for stimuli transmitted over the right nasal and right temporal pathways. The
1
TABLE 1 TESTSBETWEENVISUALHALF-FIELD (VHF) ADJUSTED RECALLSCORE MEANSFOR EACHSERIALPOSITION Serial position
Condition Right VHF Left VHF t
* p < .01; df ** p < .02; df
1
2
3
4
5
.232 ,164 4.297*
.235 ,156 4.91 1*
.229 ,172 3.069*
.2a7 ,240 2.45**
,619 ,622 ,613
= 160. = 160.
TABLE 2 ADJUSTEDRECALLSCOREMEANSFOR THE EYE BY VISUALHALF-FIELD (VHF) VIEWINGCONDITIONS WITH THE CORRESPONDING VISUALPATHWAYS Condition Right VHF Left VHF
Left eye Left temporal
Right eye Right nasal
,320
,322
Left nasal
Right temporal
.270
.272
RAY PARKER et
al.
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failure of acuity dominance to reach significance is indicative of a minimal relationship between this variable and performance on the VHF STM task.
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D. DISCUSSION The transmission of discrete, lettered stimuli has provided results which are generally consistent with present concepts of the human visual system and current theories concerning hemispheric asymmetry of function (2, 6, 13, 14). With respect to intereye variability in magnitude of right VHF superiority, the obtained results do not agree with those of McKeever and Huling (13). Such variation in results obtained with the Hines-Satz and McKeever paradigms is not surprising, since correct responding in the latter design depends very heavily on the S’s ability to recognize single stimuli presented at threshold durations. The Hines-Satz paradigm, on the other hand, employs exposure durations well above threshold and includes several stimuli on each trial. For this reason, successful report of stimuli with this latter paradigm may be primarily dependent on the S’s processing and short-term storage abilities. In this context, perceptual recognition factors may actually play a very minimal role in multiple-stimulus long-duration procedures, such as the Hines-Satz paradigm. When this hypothesis is considered together with the nonsignificant effects of acuity dominance, an explanation can be suggested for both the acuity dominance results and the absence of intereye differences in VHF asymmetry. Perhaps perceptual factors involving intereye differences in perceptual ability are more important at threshold exposure durations and do not operate with any significance in some paradigms using more lengthy presentation times. Acuity dominance might certainly be related to VHF asymmetry in this way and, on this basis, one would not expect it to influence the asymmetry to any significant extent in the Hines-Satz paradigm. However, VHF asymmetry in threshold recognition designs might be affected significantly by intra-S differences in acuity dominance. Hemispheric asymmetry of function and acuity dominance could theoretically interact in such a design to produce various intereye recall differences. Only research investigating the effects of acuity dominance at threshold durations would provide additional information.
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