Perceptual ond Motor Skills, 1979, 49, 335-338. @ Perceptual and Motor Skills 1979
A LENGTH AFTEREFFECT FROM GRATING ADAPTATION: N O W YOU SEE IT . . . N O W YOU DON'T WILLARD L. BRIGNER Appalachian Stare University1 Summary.-Adaptation to a grating of short bars has the effect of increasing the apparent length of a subsequently viewed test bar, and adaptation to a grating of long bars has the effect of decreasing the apparent length of a subsequently viewed test bar. However, decreasing the interspace between the long adaptation bars has the effect of (1) negating the length aftereffect and ( 2 ) reducing the apparent width of the test bar viewed by the retina previously adapted to the grating of long bars.
After observing a high contrast grating for a brief period, detection is impaired for a subsequently viewed low contrast grating of the same orientation and periodicity (Blakemore & Campbell, 1969; Pantle & Sekuler, 1969). This threshold elevation effect has led to the hypothesis that analysis of retinal image size is performed by visual-spatial frequency analyzers (Blakemore & Campbell, 1969; Blakemore & Sutton, 1969). To support this hypothesis, Blakemore and Sutton (1969) have provided a demonstration of the effect of grating adaptation upon perceived size. The demonstration requires an observer scan a line between two square wave gratings; one grating has narrow bars and the other broad bars. After a brief period of scanning, the observer then looks at a fixation point between two square wave gratings having bars of intermediate width. Even though the bars in the latter configuration are equal in width, the intermediate bars appear decreased in width when viewed by the retina previously used in scanning the broad bars, and bars of the same intermediate width appear increased in width when viewed by the retina previously used in scanning the narrow bars. While the effect of grating adaptation upon perceived size, as described above, concerns changes in apparent width, it should be possible to demonstrate an effect of grating adaptation upon perceived length as well, and in Part I of the current paper, a demonstration of this effect, an effect of grating adaptation upon perceived length, is presented."uch an effect is comparable to the demonstrations that length, like orientation and periodicity, influences contrast 'Boone, North Carolina 28608. 'Length aftereffects in figural aftereffects have been demonstrated. However, one should not confuse figural aftereffects with adaptation to gratings where scanning a fixation line is involved; there are obvious procedural and phenomenal differences. The procedure which characrerizes figural aftereffects is fixation of an inspection figure and subsequent viewing of a test figure. 'The fixation of the inspection figure results in an afterimage. On the other hand, the procedure which characterizes adaptation to gratings is scanning a fixation line or letting the gaze roam over the pattern. No afterimage is associated with this procedure. Figural aftereffects involve adaptation ar a specific retinal locus, i.e.. an afterimage, while scanning a grating leads to adaptation at some locus in the visual system other than the retina (Blakemore & Campbell, 1969).
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threshold elevation of a tesc grating (Nskayama & Roberts, 1972; Burton, 1976; Burton & Ruddock, 19781. The effect of grating adaptation upon perceived length, as noted above, is predictable from the theoretical account used by Blakemore and Sutton ( 1969) to explain the size aftereffect they reported; namely, adaptation of size-selective neurons results in a shift in apparent size away from the stimulus size used in adaptation. For example, if adaptation bars are smaller than tesc bars, the tesc bars are increased in apparent size. However, in Part I1 of the current paper, grating adaptation leads ro differences in perceived width, although adaptation and test bars are equal in width. Furthermore, these differences in apparent width are associated with a negation of the effect of grating adapration upon perceived length as described previously. These findings are not predictable from the Blakemore and Sutton (1969) position. Part I: A Length Aftereffect An effect of grating adaptation upon perceived length can be observed in Fig. 1. First, inspect the two bars at the top of Fig. 1 and be satisfied that they are equal in length. Then, scan the vertical line between the two gratings at the bottom of Fig. 1 for about 1 min. After the scanning period, quickly shift your gaze to the fixation point between the two bars at the top. They should no longer appear equal in length. Adaptation to the grating of short bars has the effect of making the top right bar appear increased in length, and adaptation to the grating of long bars has the effect of making the top left bar appear decreased
:1-
FIG. 1. Follow the instructions in the text to observe a length aftereffect
in length. In view of the contrast specificity of the size aftereffect ( d e Valois, 1977),%t is appropriate to confirm the effect of grating adapration upon perceived length by using test bars. Consistent with the foregoing demonstration, adaptation and test bars, as shown in Fig. 1, were presented to nine observers who were enrolled in introductory psycho!ogy courses. From a distznce of approximately 39 un.,observers "Recently, de Valois ( 1 9 7 7 ) demonstrated the contrast specificiry of grating adaptation, i.e., apparent width of white test bars was shown to be affected only by the width of white adaptation bars, and apparent width of black test bars was shown to be affected only by the width of black adaptation bars. Therefore, i t can be assumed that a grating's white interspaces d 3 not influence the perceived size of a black test bar and that changes in the perceived size of a black test bar must be attributed to factors related to the black adaptation bars.
LENGTH AFTEREFFECT
337
scanned the vertical line between the adaptation gratings for 1 min. before shifting the gaze to the fixation point between the test bars and reporting which tesc bar appeared longer. It was predicted that observers would report as longer the tesc Ear viewed by the retina previous!y used in scanning the short adaptation bars. Reports consistent with this prediction were scored as 1 or a "success,'' and reports not consistent with this prediction were to be scored as 0 or a "failure." However, all nine observers gave reports consistent with the prediction, i.e., 9 "successes" and 0 "failures," and reported as longer the test bar viewed by the retina previously adapced to short bars ( N = 9, p = ,002, binomial test). Anecdotal data indicated no perceived change in test bar width. Part 11: Negation of the Length Aftereffect The length aftereffect described above is predictable from the theoretical account used by Blakemore and Sutton (1969) to explain the size aftereffect they reported, namely, adaptation of size-selective neurons results in a shift in apparent size away from the stimulus size used in adaptation. For example, large adaptation bars have the effect of diminishing the apparent size of test bars smaller than the adaptation bars. However, the following phenomena are not predictable from their theoretical position: uiz., ( 1 ) there is a change in perceived width even though the adaptation and test bars are equal in width; ( 2 ) the change in apparent width negates the length aftereffect. These phenomena can be observed in Fig. 2.
Frc. 2. Follow the instructions in the
--
'I=
text to observe a change in the apparent width of the upper test bars. Despite the similarity to the configuration in Fig. 1. rhere is no length aftereffect.
I
As before, inspect the two bars at the top of Fig. 2 and be satisfied that they are equal in length and width. (Note: If there appear to be differences in the two bars, there is a residual aftereffect from the prior demonstration; therefore, additional time must be allowed for the prior aftereffect to dissipate before the current phenomena can be observed.) Next, scan the vertical line benveen the two gratings at the bottom of Fig. 2 for about one minute. Then, quickly shift your gaze to the fixation point between the two bars at the top. The top lefc bar should Rppear narrower than the right bar, and rhere should be no perceived differences in length despite the similarity of the adapting configuration to that used in Part I demonstrating a length aftereffect. In keeping with the foregoing demonstration, adaptation and tesc bars, as shown in Fig. 2, were presented to 12 observers who were recruited from intro-
3 38
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ductory courses in psychology. The viewing distance and scanning period were the same as those reported in Part I. After grating adaptation, an observer reported which test bar appeared narrower and which test bar appeared longer. If the observer reported as narrower the test bar viewed by the retina previously adapted to the long bars, chis was scored a "success" or 1; reports contrary to this were scored "failure" or 0. All observers reported as narrower the test bar viewed by the retina previously adapted to long bars, i.e., 12 "successes" and 0 "failures" (N= 12, p < ,001, binomial test). If an observer reported as longer the test bar viewed by the retina previously adapted to short bars, this was scored a "success" or 1; reports contrary to this were scored "failure" or 0. Seven observers reported as longer the test bar viewed by the retina previously adapted to short bars, i.e., 7 "successes" and 5 "failures" ( N = 12, p = .387, binomial test). Contrary to the findings in Part I, the report of a length aftereffect occurred no more frequently than may be expected by chance. In summary, Part I presented a length aftereffect which generally supports the theory that analysis of retinal-image size may be performed by visual-spatial frequency analyzers. On the other hand, Part I1 presented a slightly modified adaptation configuration which had the effect of negating the length aftereffect and of producing perceived width differences. The latter demonstration would suggest that an appropriate model for analysis of retinal-image size must incorporate some form of length-width interaction. Interaction between perceived length and perceived width has also been reported by Waite and Massaro ( 1970). As presented by Blakemore and Campbell ( 1969) and Blakemore and Sutton (1969), the spatial frequency analyzer model does not predict lengthwidth interaction. These and other data (Brigner, 1977) create uncertainty about the role of visual-spatial frequency analysis in the perception of extent. REFERENCES BLAKEMORE, C., & CAMPBELL, F. W. On the existence of neurons in the human visual system selectively sensitive to the orienration and size of retinal images. I . Physiol., Lond., 1969, 203, 237-260.
BLAKEMORE, C., & SUTTON,P. Size adaptation: a new aftereffect. Science, 1969, 166,
245-247. BRIGNER,W. L. A special spatial frequency analyzer. Vision Res., 1977, 17, 1241. BURTON,G. J. Visual detection of patterns periodic in two-dimensions. Vision Res., 1976, 16, 991-998. BURTON, G. J., & RUDDOCK, K. H. Visual adaptation to patterns conraining two-dimensional spatial structure. Vision Res., 1978, 18, 93-99. NAKAYAMA, K., & ROBERTS, D. J. Line-lengrh detectors in the human visual system: evidence from selective adaptation. Vision Rer., 1972, 12, 1709-1713. PANTLE, A,, & SEKULER, R. COntrast responses of human visual mechanisms sensitive to orientarion and direction of motion. Vision Res., 1969, 9, 397-406. DE VALOIS. K. K. Independence of black and white: phase-specific adaptation. Vision Res., 1977, 17, 209-215. WAITE,H., & MASSARO, D. W. Test of Gregory's constancy scaling explanation of the Mullet-Lyer illusion. Natwe, 1970, 227, 733-734. Accepted July 30, 1979.
A LENGTH AFTEREFFECT FROM GRATING ADAPTATION: N O W YOU SEE IT . . . N O W YOU DON'T WILLARD L. BRIGNER Appalachian Stare University1 Summary.-Adaptation to a grating of short bars has the effect of increasing the apparent length of a subsequently viewed test bar, and adaptation to a grating of long bars has the effect of decreasing the apparent length of a subsequently viewed test bar. However, decreasing the interspace between the long adaptation bars has the effect of (1) negating the length aftereffect and ( 2 ) reducing the apparent width of the test bar viewed by the retina previously adapted to the grating of long bars.
After observing a high contrast grating for a brief period, detection is impaired for a subsequently viewed low contrast grating of the same orientation and periodicity (Blakemore & Campbell, 1969; Pantle & Sekuler, 1969). This threshold elevation effect has led to the hypothesis that analysis of retinal image size is performed by visual-spatial frequency analyzers (Blakemore & Campbell, 1969; Blakemore & Sutton, 1969). To support this hypothesis, Blakemore and Sutton (1969) have provided a demonstration of the effect of grating adaptation upon perceived size. The demonstration requires an observer scan a line between two square wave gratings; one grating has narrow bars and the other broad bars. After a brief period of scanning, the observer then looks at a fixation point between two square wave gratings having bars of intermediate width. Even though the bars in the latter configuration are equal in width, the intermediate bars appear decreased in width when viewed by the retina previously used in scanning the broad bars, and bars of the same intermediate width appear increased in width when viewed by the retina previously used in scanning the narrow bars. While the effect of grating adaptation upon perceived size, as described above, concerns changes in apparent width, it should be possible to demonstrate an effect of grating adaptation upon perceived length as well, and in Part I of the current paper, a demonstration of this effect, an effect of grating adaptation upon perceived length, is presented."uch an effect is comparable to the demonstrations that length, like orientation and periodicity, influences contrast 'Boone, North Carolina 28608. 'Length aftereffects in figural aftereffects have been demonstrated. However, one should not confuse figural aftereffects with adaptation to gratings where scanning a fixation line is involved; there are obvious procedural and phenomenal differences. The procedure which characrerizes figural aftereffects is fixation of an inspection figure and subsequent viewing of a test figure. 'The fixation of the inspection figure results in an afterimage. On the other hand, the procedure which characterizes adaptation to gratings is scanning a fixation line or letting the gaze roam over the pattern. No afterimage is associated with this procedure. Figural aftereffects involve adaptation ar a specific retinal locus, i.e.. an afterimage, while scanning a grating leads to adaptation at some locus in the visual system other than the retina (Blakemore & Campbell, 1969).
336
W. L. BRIGNER
threshold elevation of a tesc grating (Nskayama & Roberts, 1972; Burton, 1976; Burton & Ruddock, 19781. The effect of grating adaptation upon perceived length, as noted above, is predictable from the theoretical account used by Blakemore and Sutton ( 1969) to explain the size aftereffect they reported; namely, adaptation of size-selective neurons results in a shift in apparent size away from the stimulus size used in adaptation. For example, if adaptation bars are smaller than tesc bars, the tesc bars are increased in apparent size. However, in Part I1 of the current paper, grating adaptation leads ro differences in perceived width, although adaptation and test bars are equal in width. Furthermore, these differences in apparent width are associated with a negation of the effect of grating adapration upon perceived length as described previously. These findings are not predictable from the Blakemore and Sutton (1969) position. Part I: A Length Aftereffect An effect of grating adaptation upon perceived length can be observed in Fig. 1. First, inspect the two bars at the top of Fig. 1 and be satisfied that they are equal in length. Then, scan the vertical line between the two gratings at the bottom of Fig. 1 for about 1 min. After the scanning period, quickly shift your gaze to the fixation point between the two bars at the top. They should no longer appear equal in length. Adaptation to the grating of short bars has the effect of making the top right bar appear increased in length, and adaptation to the grating of long bars has the effect of making the top left bar appear decreased
:1-
FIG. 1. Follow the instructions in the text to observe a length aftereffect
in length. In view of the contrast specificity of the size aftereffect ( d e Valois, 1977),%t is appropriate to confirm the effect of grating adapration upon perceived length by using test bars. Consistent with the foregoing demonstration, adaptation and test bars, as shown in Fig. 1, were presented to nine observers who were enrolled in introductory psycho!ogy courses. From a distznce of approximately 39 un.,observers "Recently, de Valois ( 1 9 7 7 ) demonstrated the contrast specificiry of grating adaptation, i.e., apparent width of white test bars was shown to be affected only by the width of white adaptation bars, and apparent width of black test bars was shown to be affected only by the width of black adaptation bars. Therefore, i t can be assumed that a grating's white interspaces d 3 not influence the perceived size of a black test bar and that changes in the perceived size of a black test bar must be attributed to factors related to the black adaptation bars.
LENGTH AFTEREFFECT
337
scanned the vertical line between the adaptation gratings for 1 min. before shifting the gaze to the fixation point between the test bars and reporting which tesc bar appeared longer. It was predicted that observers would report as longer the tesc Ear viewed by the retina previous!y used in scanning the short adaptation bars. Reports consistent with this prediction were scored as 1 or a "success,'' and reports not consistent with this prediction were to be scored as 0 or a "failure." However, all nine observers gave reports consistent with the prediction, i.e., 9 "successes" and 0 "failures," and reported as longer the test bar viewed by the retina previously adapced to short bars ( N = 9, p = ,002, binomial test). Anecdotal data indicated no perceived change in test bar width. Part 11: Negation of the Length Aftereffect The length aftereffect described above is predictable from the theoretical account used by Blakemore and Sutton (1969) to explain the size aftereffect they reported, namely, adaptation of size-selective neurons results in a shift in apparent size away from the stimulus size used in adaptation. For example, large adaptation bars have the effect of diminishing the apparent size of test bars smaller than the adaptation bars. However, the following phenomena are not predictable from their theoretical position: uiz., ( 1 ) there is a change in perceived width even though the adaptation and test bars are equal in width; ( 2 ) the change in apparent width negates the length aftereffect. These phenomena can be observed in Fig. 2.
Frc. 2. Follow the instructions in the
--
'I=
text to observe a change in the apparent width of the upper test bars. Despite the similarity to the configuration in Fig. 1. rhere is no length aftereffect.
I
As before, inspect the two bars at the top of Fig. 2 and be satisfied that they are equal in length and width. (Note: If there appear to be differences in the two bars, there is a residual aftereffect from the prior demonstration; therefore, additional time must be allowed for the prior aftereffect to dissipate before the current phenomena can be observed.) Next, scan the vertical line benveen the two gratings at the bottom of Fig. 2 for about one minute. Then, quickly shift your gaze to the fixation point between the two bars at the top. The top lefc bar should Rppear narrower than the right bar, and rhere should be no perceived differences in length despite the similarity of the adapting configuration to that used in Part I demonstrating a length aftereffect. In keeping with the foregoing demonstration, adaptation and tesc bars, as shown in Fig. 2, were presented to 12 observers who were recruited from intro-
3 38
W. L. BRIGNER
ductory courses in psychology. The viewing distance and scanning period were the same as those reported in Part I. After grating adaptation, an observer reported which test bar appeared narrower and which test bar appeared longer. If the observer reported as narrower the test bar viewed by the retina previously adapted to the long bars, chis was scored a "success" or 1; reports contrary to this were scored "failure" or 0. All observers reported as narrower the test bar viewed by the retina previously adapted to long bars, i.e., 12 "successes" and 0 "failures" (N= 12, p < ,001, binomial test). If an observer reported as longer the test bar viewed by the retina previously adapted to short bars, this was scored a "success" or 1; reports contrary to this were scored "failure" or 0. Seven observers reported as longer the test bar viewed by the retina previously adapted to short bars, i.e., 7 "successes" and 5 "failures" ( N = 12, p = .387, binomial test). Contrary to the findings in Part I, the report of a length aftereffect occurred no more frequently than may be expected by chance. In summary, Part I presented a length aftereffect which generally supports the theory that analysis of retinal-image size may be performed by visual-spatial frequency analyzers. On the other hand, Part I1 presented a slightly modified adaptation configuration which had the effect of negating the length aftereffect and of producing perceived width differences. The latter demonstration would suggest that an appropriate model for analysis of retinal-image size must incorporate some form of length-width interaction. Interaction between perceived length and perceived width has also been reported by Waite and Massaro ( 1970). As presented by Blakemore and Campbell ( 1969) and Blakemore and Sutton (1969), the spatial frequency analyzer model does not predict lengthwidth interaction. These and other data (Brigner, 1977) create uncertainty about the role of visual-spatial frequency analysis in the perception of extent. REFERENCES BLAKEMORE, C., & CAMPBELL, F. W. On the existence of neurons in the human visual system selectively sensitive to the orienration and size of retinal images. I . Physiol., Lond., 1969, 203, 237-260.
BLAKEMORE, C., & SUTTON,P. Size adaptation: a new aftereffect. Science, 1969, 166,
245-247. BRIGNER,W. L. A special spatial frequency analyzer. Vision Res., 1977, 17, 1241. BURTON,G. J. Visual detection of patterns periodic in two-dimensions. Vision Res., 1976, 16, 991-998. BURTON, G. J., & RUDDOCK, K. H. Visual adaptation to patterns conraining two-dimensional spatial structure. Vision Res., 1978, 18, 93-99. NAKAYAMA, K., & ROBERTS, D. J. Line-lengrh detectors in the human visual system: evidence from selective adaptation. Vision Rer., 1972, 12, 1709-1713. PANTLE, A,, & SEKULER, R. COntrast responses of human visual mechanisms sensitive to orientarion and direction of motion. Vision Res., 1969, 9, 397-406. DE VALOIS. K. K. Independence of black and white: phase-specific adaptation. Vision Res., 1977, 17, 209-215. WAITE,H., & MASSARO, D. W. Test of Gregory's constancy scaling explanation of the Mullet-Lyer illusion. Natwe, 1970, 227, 733-734. Accepted July 30, 1979.
