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R H Day

Publications and source records attributed to R H Day.

At least 19 recordsLinked to original sources
PubMed1992

Two movement aftereffects: evidence for luminance- and color-movement pathways.

Two movement aftereffects (MAEs) that bear closely on the issue of visual processing of color and movement have been isolated. Following adaptation with a vertical luminance stimulus a strong MAE occurred with the same stationary test stimulus oriented horizontally and also in a perfectly uniform field. Neither effect occurred following adaptation with a color equiluminance stimulus. These aftereffects have not been reported before. It is concluded that there are at least three pathways for movement, a color, a color-plus-luminance, and a luminance pathway.

Adaptation, Ocular↗
PubMed1992

The Müller-Lyer illusion Mark II.

A new illusion of size is described. A passage of print occupying about half a standard A4 sheet appeared larger than the same passage when the sheet was cropped immediately above and below it. This illusion is demonstrated and explained in terms of perceptual compromise between the vertical extent of the printed passage and the sheet of which it is an intrinsic feature. In this sense it is held to be essentially the same as the Müller-Lyer illusion of extent in which the spaces between the apexes are intrinsic to the figure.

Attention↗
PubMed1992

The Poggendorff illusion and apparent interparallel extents.

An explanation of the Poggendorff misalignment effect in terms of apparent contraction of interparallel extent resulting from the Müller-Lyer illusion was tested in three experiments. Three of the eight stimulus figures had oblique transversals outside the parallels in the usual way, three had them inside, and two were controls consisting of the transversals only. Müller-Lyer forms were differently delineated between the parallels for the inside-transversal and outside-transversal figures, and were not delineated in the control figures. In the first experiment apparent misalignment occurred in four of the six parallel-line figures and in neither of the controls. In the second experiment oblique extent between the parallels was underestimated in six of the eight figures and right-angle extent was overestimated in all of them. The results of the third experiment showed that right-angle (horizontal) extent between the parallels without transversals is estimated without significant error. The data from the three experiments do not support the interparallel-extent explanation of apparent misalignment. Instead, the results are interpreted in terms of independent perceptual compromises, one involving alignment of the transversals and the other the distance between them.

Adult↗
PubMed1992

The effect of accommodation on retinal image size.

The apparent size of an object is diminished when accommodation of the eye moves inward to a position closer to the observer than to a viewed object. This phenomenon is called accommodation micropsia. Using schematic eyes, we investigated change in retinal image size caused by a change in accommodation. The use of schematic eyes is also discussed and is justified. The calculated magnitude of this diminution for four schematic eyes ranged from unity at infinity to a maximum of 0.98 (-2%) at about 12.0 diopters (D). For distances at which accommodation micropsia is typically observed (about 2.0 D), retinal minification is less than 0.997 (-0.3%). Thus changes in the size of the retinal image attributable to accommodation are virtually negligible when compared with the observed reduction of 3% to 33%. This suggests that accommodation micropsia is mediated almost entirely by processes other than those involving the optics of the eye.

Accommodation, Ocular↗
PubMed1992

Spatial-frequency-contingent color aftereffects: adaptation with one-dimensional stimuli.

The McCollough effect was shown to be spatial-frequency selective by Lovegrove and Over (1972) after adaptation with vertical colored square-wave gratings separated by 1 octave. Adaptation with slide-presented red and green vertical square-wave gratings separated by 1 octave failed to produce contingent color aftereffects (CAEs). However, when each of these gratings was adapted alone, strong CAEs were produced. Adaptation with vertical colored sine-wave gratings separated by 1 octave also failed to produce CAEs, but strong effects were produced by adaptation with each grating alone. By varying the spatial frequency of the test sine wave, CAEs were found to be tuned for spatial frequency at 2.85 octaves after adaptation of 4 cycles per degree (cpd) and at 2.30 octaves after adaptation of 8 cpd. Adaptation of both vertical and horizontal sine-wave gratings produced strong CAEs, with bandwidths ranging from 1.96 to 2.90 octaves and with lower adapting contrast producing weaker CAEs. These results indicate that the McCollough effect is more broadly tuned for spatial frequency than are simple adaptation effects.

Adaptation, Ocular↗
PubMed1992

Spatial-frequency-contingent color aftereffects: adaptation with two-dimensional stimulus patterns.

The spatial-frequency theory of vision has been supported by adaptation studies using checkerboards in which contingent color aftereffects (CAEs) were produced at fundamental frequencies oriented at 45 degrees to the edges. A replication of this study failed to produce CAEs at the orientation of either the edges or the fundamentals. Using a computer-generated display, no CAEs were produced by adaptation of a square or an oblique checkerboard. But when one type of checkerboard (4 cpd) was adapted alone, CAEs were produced on the adapted checkerboard and on sine-wave gratings aligned with the fundamental and third harmonics of the checkerboard spectrum. Adaptation of a coarser checkerboard (0.80 cpd) produced CAEs aligned with both the edges and the harmonic frequencies. With checkerboards of both frequencies, CAEs were also found on the other type of checkerboard that had not been adapted. This observation raises problems for any edge-detector theory of vision, because there was no adaptation to edges. It was concluded that spatial-frequency mechanisms are operating at both low- and high-spatial frequencies and that an edge mechanism is operative at lower frequencies. The implications of these results are assessed for other theories of spatial vision.

Adaptation, Ocular↗
PubMed1992

Integration of sequential information for shape perception by infants: a developmental study.

Perception of form by spatiotemporal integration was investigated in 3 experiments. In the first, infants aged 8, 10, and 12 months were tested using a novelty-preference procedure to determine the earliest age at which recognition of rectilinear and curvilinear form occurred. Infants were shown a light-point tracing of the outline of a figure, followed by simultaneous presentation of 2 test objects, one of the same shape as the tracing and one of a different shape. The tracing was double the size of the test objects. Only infants in the oldest group responded selectively by looking longer at the object of different shape. In the second experiment with 12-month-old infants only, it was shown that recognition of rectilinear, but not curvilinear, form occurred despite a difference in the orientation and size of tracing and object. Computer-generated tracings were used in the final experiment to compare form recognition for 2D and 3D stimuli. Selective responding occurred only for the latter. These findings show that by 12 months infants perceive the correspondence between the figural properties of a tracing and its extended form, but that this perception is dependent on the provision of depth cues.

Cognition↗
PubMed1991

Sine of an illusion.

In an informally observed sine-wave figure in which the vertical extent between contours was constant, apparent extent in the crest and trough (the 'turns') appeared greater than in the straight oblique sections of the figure. This observation was confirmed in two experiments in which the vertical extents were matched by two vertically arranged dots. It was found that in a turn the apparent extent was greater than the true extent, but in a straight section both extents were about equal. These outcomes were confirmed when the two sections were each separated from the figure and presented alone. The illusion is explained in terms of a perceptual compromise between the vertical extent and the greater overall dimensions of the section at the turn of the sine-wave figure and is thereby held to be the same in principle as the Müller-Lyer illusion.

Adult↗
PubMed1991

The Fraser illusion: complex figures.

The cause of the Fraser illusion, which occurs when a line made up of tilted segments itself appears tilted, is examined further. In this series of experiments, we used figures that resembled the original Fraser illusion; they were more complex than those reported on in our previous paper (Stuart & Day, 1988). The figures were used to explore two theories of the Fraser illusion further: that it is the result of interactions between orientation selective units, and that it is a consequence of the local, distributed processing of orientation. The presence of background elements like those used in the original illusion led to an increase in the strength of the illusion, but the shape of these elements had no differential effect on illusion strength. There was a differential effect of the background on the assimilative and contrast illusions, owing respectively to small and large tilts of the inducing elements. The illusion was markedly reduced at small visual angles when the background was absent, but it was only slightly affected when the background was present. All these findings are difficult to explain in terms of interactions between single units, either at the same or at different scales in the image. The effects of luminance contrast and isoluminance on the illusion were not consistent with either theory, but they indicated that researchers need to consider the role of figure-ground organization in this illusion.

Adolescent↗
PubMed1990

Perceived causality occurs with stroboscopic movement of one or both stimulus elements.

It was shown by magnitude estimation that the perception of causality first described by Michotte (1946/1963) also occurs consistently and strongly with stroboscopic, ie apparent or phi, movement. This is so when the 'causal' movement is stroboscopic and the 'caused' movement real, when these movements are reversed, and when both movements are stroboscopic. The effect is not due to prior experience with Michotte-type displays.

Adult↗
PubMed1990

The Bourdon illusion occurs with straight-, right-angle-, and parallel-edge figures.

The Bourdon illusion is the apparent bentness of the straight edge of a figure consisting of two elongated triangular components arranged apex to apex. In three experiments, the illusion was shown to occur in the opposite direction, with the components arranged base to base. It was also shown to occur with the component edges at right angles and parallel. With the edges at right angles, the illusion also occurred in one direction when the components were apex to apex and occurred in the opposite direction when they were base to base. Supplementary observations indicated that the illusion is stronger when the components are relatively small and widely separated and eliminated when one of the two edges is curved.

Adult↗
PubMed1990

The Bourdon illusion in haptic space.

A strong Bourdon illusion-the apparent bentness of a straight edge-in the active haptic mode was established in two experiments. Blindfolded subjects clasped the opposite surfaces of an object with the same frontal profile as the visual figure between thumb and forefinger and moved the latter together from end to end across the object. When the two triangular components of the objects were rotated through 180 degrees so that their bases instead of their apexes were contiguous, the illusion was reversed in direction and reduced by about half, as with the visual illusion. It was concluded that the active haptic Bourdon illusion is basically the same as the visual illusion and can be accounted for by a compromise in perception between the orientation of the test surface and that of the object of which it is an integral part.

Adult↗
PubMed1990

Do infants use their own images to locate objects reflected in a mirror?

The ability of infants to locate a toy from a mirror reflection was investigated in 3 experiments. In the first, it was found that a minority of 22-month-old infants turned to locate the toy that was the source of the reflection, and that localization of the toy occurred regardless of whether the infants' own image was visible in the mirror. The results of 2 further experiments indicated that younger infants aged 14 and 18 months rarely use mirror information to locate a toy. When they do so, they also turn whether or not images of themselves are visible. It is concluded that tasks involving the localization of objects or events from mirror images are not direct indices of self-recognition. Rather, they indicate the skill of infants in using the mirror as a perceptual tool.

Arousal↗
PubMed1989

Visual misalignment in arc and chevron figures.

Five experiments investigated an apparent misalignment effect in 90 degrees arc figures. Preliminary observations showed that the effect occurs also in chevron figures, in an afterimage of the arc figure, and haptically in arc- and chevron-shaped objects. The experiments showed that the effect is greater with 3 radial lines than with 2, absent without them, and present in a figure consisting of only 3 radial lines. The effect with arc figures was consistently greater than that with chevron figures, a difference found not to be due to an apex marking the midpoint of the latter, and it was of intermediate size in figures with 1 arc boundary and 1 chevron boundary. The misalignment was also greater in narrow, elongated figures. The issues singled out for discussion are the effect of context on the misalignment effect with 3 radial lines, a possible explanation in terms of perceptual compromise, the difference in the effect between arcs and chevrons, and the relationship between this illusion and the Morinaga illusion.

Adult↗
PubMed1989

Negative afterimages and the McCollough effect.

Four experiments were conducted to test earlier claims about the relationship between the negative afterimage and the McCollough effect. The first claim (Hansel & Mahmud, 1978) is that long-lasting afterimages occur when induced by the same alternating-stimulus procedure as that used to induce the McCollough effect. The second claim (Murch & Hirsch, 1972) is that afterimages can themselves induce McCollough effects if they are induced and paired sequentially with grating patterns. In testing these claims, a reliable computer-controlled color-cancellation technique developed earlier was used to measure the apparent color of both afterimages and McCollough effects objectively. No support was found for the first claim following alternative presentation of two homogeneously colored regions for total periods of 5 min (Experiment 1) and 20 min (Experiment 2). The second claim was fully supported: After an induction period of 7.3 min, a McCollough effect occurred for a red-vertical pairing but not for a green-horizontal pairing (Experiment 3); but after an induction period of 20 min, McCollough effects occurred strongly for both pairings (Experiment 4). The theoretical implications of these outcomes are considered in the context of recent theories of color and pattern processing in the visual system.

Adult↗