Apparent velocity of motion aftereffects in central and peripheral vision

Adapting to a drifting grating (temporal frequency 4 Hz, contrast 0.4) in the periphery gave rise to a motion aftereffect (MAE) when the grating was stopped. A standard unadapted foveal grating was matched to the apparent velocity of the MAE, and the matching velocity was approximately constant regardless of the visual field position and spatial frequency of the adapting grating. On the other hand, when the MAE was measured by nulling with real motion of the test grating, nulling velocity was found to increase with eccentricity. The nulling velocity was constant when scaled to compensate for changes in the spatial 'grain' of the visual field. Thus apparent velocity of MAE is constant across the visual field, but requires a greater velocity of real motion to cancel it in the periphery. This confirms that the mechanism underlying MAE is spatially-scaled with eccentricity, but temporally homogeneous. A further indication of temporal homogeneity is that when MAE is tracked, by matching or by nulling, the time course of temporal decay of the aftereffect is similar for central and for peripheral stimuli.     

The auditory motion aftereffect: its tuning and specificity in the spatial and frequency domains

In this paper, the auditory motion aftereffect (aMAE) was studied, using real moving sound as both the adapting and the test stimulus. The sound was generated by a loudspeaker mounted on a robot arm that was able to move quietly in three-dimensional space. A total of 7 subjects with normal hearing were tested in three experiments. The results from Experiment 1 showed a robust and reliable negative aMAE in all the subjects. After listening to a sound source moving repeatedly to the right, a stationary sound source was perceived to move to the left. The magnitude of the aMAE tended to increase with adapting velocity up to the highest velocity tested (20 degrees/sec). The aftereffect was largest when the adapting and the test stimuli had similar spatial location and frequency content. Offsetting the locations of the adapting and the test stimuli by 20 degrees reduced the size of the effect by about 50%. A similar decline occurred when the frequency of the adapting and the test stimuli differed by one octave. Our results suggest that the human auditory system possesses specialized mechanisms for detecting auditory motion in the spatial domain.     

The auditory motionaftereffect: Its tuning and specificity in the spatial and frequency domains

In this paper, the auditory motion aftereffect (aMAE) was studied, using real moving sound as both the adapting and the test stimulus. The sound was generated by a loudspeaker mounted on a robot arm that was able to move quietly in three-dimensional space. A total of 7 subjects with normal hearing were tested in three experiments. The results from Experiment 1 showed a robust and reliable negative aMAE in all the subjects. After listening to a sound source moving repeatedly to the right, a stationary sound source was perceived to move to the left. The magnitude of the aMAE tended to increase with adapting velocity up to the highest velocity tested (20°/sec). The aftereffect was largest when the adapting and the test stimuli had similar spatial location and frequency content. Offsetting the locations of the adapting and the test stimuli by 20° reduced the size of the effect by about 50%. A similar decline occurred when the frequency of the adapting and the test stimuli differed by one octave. Our results suggest that the human auditory system possesses specialized mechanisms for detecting auditory motion in the spatial domain.     

Effects of orientation-selective adaptation on the Z?llner illusion

The model of inhibitory interaction between orientation detectors was examined by prolonged presentation of grating patterns (which was expected to induce orientation-selective adaptation) before measurement of the Z?llner illusion. Adaptation effects were measured under conditions which excluded intrusion by the tilt aftereffect. In experiment 1, illusion magnitude greatly decreased only when the orientation of the adapting grating was the same as that of the inducing lines, which confirmed the first prediction deduced from the model. There was no effect of adapting grating when it was oriented more than 20 degrees away from the inducing lines. In experiment 2, adaptation effects were selective not only to orientation but also to spatial frequency. In experiment 3 it was shown that illusion reduction was mediated neither by lowered apparent contrast of the inducing lines nor by retinal adaptation. The results are discussed with respect to the nature of adaptation and possible physiological correlates.     

Contextual modulation of the motion aftereffect

The authors examined center-surround effects for motion perception in human observers. The magnitude of the motion aftereffect (MAE) elicited by a drifting grating was measured with a nulling task and with a threshold elevation procedure. A surround grating of the same spatial frequency, temporal frequency, and orientation significantly reduced the magnitude of the MAE elicited by adaptation to the center grating. This effect was bandpass tuned for spatial frequency, orientation, and temporal frequency. Plaid surrounds but not contrast-modulated surrounds that moved in the same direction also reduced the MAE. These results provide psychophysical evidence for center-surround interactions analogous to those previously observed in electrophysiological studies of motion processing in primates. Collectively, these results suggest that motion processing, similar to texture processing, is organized for the purpose of highlighting regions of directional discontinuity in retinal images.     

Pressure blindness and the interocular transfer of size aftereffects

After observation of a stimulus composed of a top grating with large bar widths (low spatial frequency) and a bottom grating of narrow lines (high spatial frequency), a subsequently presented test grating of medium bar width appears to have a higher spatial frequency on the top half than on the bottom. Although this size aftereffect can be obtained dichoptically, this does not necessarily imply a central locus, since retinal input from the adapted eye could produce the effect. Ss were tested for the aftereffect in the adapted eye and for interocular transfer with and without pressure blinding the adapted eye. In this last condition, input from the adapted eye cannot reach the cortex. However, the aftereffect was equally present under all three conditions. This result suggests that size and frequency adaptation have a central locus.     

Contrast and frequency competition for orientation-contingent color aftereffects

A “competition” paradigm was developed to examine separately the effects of pattern contrast and spatial frequency characteristics on the strength of orientation-contingent color aftereffects (McCollough effects). After adapting to alternately presented red/black and green/black square-wave gratings (one horizontal, one vertical), 11 subjects viewed seven different kinds of test patterns. Unlike Standard McCollough effect test stimuli, the present patterns had variable luminance profiles running both horizontally and vertically within each test pattern area. Forced choice responses were used to determine which aftereffect color (red or green) appeared, as characteristics of vertical and horizontal luminance profiles were varied separately among test stimulus types. We conclude that pattern contrast and human contrast sensitivity account for aftereffect colors in such stimuli. When contrast is taken into consideration, aftereffects are not predicted by similarity between adaptation and test pattern Fourier characteristics, nor are they predicted by the width, per se, of pattern elements.     

Color-luminance relationships and the McCollough effect

The McCollough effect is an orientation-specific color aftereffect induced by adapting to colored gratings. We examined how the McCollough effect depends on the relationships between color and luminance within the inducing and test gratings and compared the aftereffects to the color changes predicted from selective adaptation to different color-luminance combinations. Our results suggest that the important contingency underlying the McCollough effect is between orientation and color-luminance direction and are consistent with sensitivity changes within mechanisms tuned to specific color-luminance directions. Aftereffects are similar in magnitude for adapting color pairs that differ only in S cone excitation or L and M cone excitation, and they have a similar dependence on spatial frequency. In particular, orientation-specific aftereffects are induced for S cone colors even when the grating frequencies are above the S cone resolution limit. Thus, the McCollough effect persists even when different cone classes encode the orientation and color of the gratings.     

Color—luminance relationships and the McCollough effect

The McCollough effect is an orientation-specific color aftereffect induced by adapting to colored gratings. We examined how the McCollough effect depends on the relationships between color and luminance within the inducing and test gratings and compared the aftereffects to the color changes predicted from selective adaptation to different color—luminance combinations. Our results suggest that the important contingency underlying the McCollough effect is between orientation and color—luminance direction and are consistent with sensitivity changes within mechanisms tuned to specific color—luminance directions. Aftereffects are similar in magnitude for adapting color pairs that differ only in S cone excitation or L and M cone excitation, and they have a similar dependence on spatial frequency. In particular, orientation-specific aftereffects are induced for S cone colors even when the grating frequencies are above the S cone resolution limit. Thus, the McCollough effect persists even when different cone classes encode the orientation and color of the gratings.     

Brightness selectivity in the motion aftereffect

Eighteen Ss were required to track the apparent motion of a stationary grating viewed after prolonged inspection of a moving grating. Measures were obtained with the inspection and test gratings identical in contrast but different in space-average luminance, or with luminance held constant and contrast varied. The aftereffect was reduced as the gratings differed in space-average luminance, but contrast exerted less uniform influence as a variable. Brightness-selectivity in the motion aftereffect is interpreted within the selective adaptation model of aftereffects as evidence that some detectors in human vision are conjointly tuned to space-average luminance and image motion.     

Evidence for a common motion mechanism of luminance-modulated and contrast-modulated patterns: selective adaptation.

Selective adaptation effects were measured with contrast-modulated patterns and sine-wave gratings in order to determine the extent to which the two patterns are processed by common mechanisms. Direction-specific adaptation effects were measured for a contrast-modulated adapting pattern and a test pattern. The contrast-modulated adapting pattern was composed of a sine-wave grating of 8 cycles deg-1 whose contrast was spatially modulated by a sinusoid of 1 cycle deg-1 at one of four levels: 100%, 60%, 30%, or 0%. The results showed that contrast-modulation thresholds for contrast-modulated gratings were raised by 0.3 to 0.5 log units following adaptation to a contrast-modulated grating moving in the same direction as the test pattern, relative to thresholds obtained following adaptation to a contrast-modulated grafting moving in the opposite direction. Cross-adaptation effects were also measured with a sine-wave adapting pattern and a contrast-modulated test pattern. The sine-wave adapting pattern was a sine-wave grating of 1 cycle deg-1 whose contrast was set to one of three levels: 16.4%, 1.25%, or 0%. The contrast-modulated test pattern was a sine-wave grating of 8 cycles deg-1 whose contrast was modulated by a sinusoid of 1 cycle deg-1. The results revealed that contrast-modulation thresholds for contrast-modulated gratings were raised by approximately 0.25 log units following adaptation to moving sine-wave gratings, relative to thresholds obtained following adaptation to a uniform field. Cross-adaptation effects were also obtained with a contrast-modulated adapting pattern and a sine-wave test pattern. The results support the view that signals generated from luminance-domain stimuli and from contrast-domain stimuli are processed by a common motion mechanism.     

Outflow and inflow in movement duplication

Following prolonged exposure to two vertical grating patterns differing in spatial frequency—one pattern illuminated in green light alternated with the other pattern illuminated in red light—human observers will sometimes report seeing desaturated complementary colors when presented with a neutrally illuminated test field consisting of adjacent halves of the two adapting gratings. The number of such color reports increases as the difference between the spatial frequencies of the adapting gratings increases. This frequency-specific chromatic aftereffect is similar to that obtained with orientation-specific color adaptation and may be mediated by neural “channels,” sensitive to both color and frequency input, which are similar to units known to exist in the visual systems of lower organisms.     

The Spectrally Dependent Monotic Component in the Decreasing-Loudness Aftereffect: Implications for Dynamic Auditory Localization

Listeners exposed to a tone increasing in intensity report an aftereffect of decreasing loudness in a steady tone heard afterward. In the present study, the spectral dependence of the monotic decreasing-loudness aftereffect (adapting and testing 1 ear) was compared with (a) the spectral dependence of the interotic decreasing-loudness aftereffect (adapting 1 ear and testing the other ear) and (b) a non-adaptation control condition. The purpose was to test the hypothesis that the decreasing-loudness aftereffect may concern the sensory processing associated with dynamic localization. The hypothesis is based on two premises: (a) dynamic localization requires monaural sensory processing, and (b) sensory processing is reflected in spectral selectivity. Hence, the hypothesis would be supported if the monotic aftereffect were more spectrally dependent and stronger than the interotic aftereffect; A. H. Reinhardt-Rutland (1998) showed that the hypothesis is supported with regard to the related increasing-loudness aftereffect. Two listeners were exposed to a 1-kHz adapting stimulus. From responses of “growing softer” or “growing louder” to test stimuli changing in intensity, nulls were calculated; test carrier frequencies ranged from 0.5 kHz to 2 kHz. Confirming the hypothesis, the monotic aftereffect peaked at around the 1-kHz test carrier frequency. In contrast, the interotic aftereffect showed little evidence of spectrally dependent peaking. Except when test and adaptation carrier frequencies differed markedly, the interotic aftereffect was smaller than the monotic aftereffect.     

The spectrally dependent monotic component in the decreasing-loudness aftereffect: implications for dynamic auditory localization

Listeners exposed to a tone increasing in intensity report an aftereffect of decreasing loudness in a steady tone heard afterward. In the present study, the spectral dependence of the monotic decreasing-loudness aftereffect (adapting and testing 1 ear) was compared with (a) the spectral dependence of the interotic decreasing-loudness aftereffect (adapting 1 ear and testing the other ear) and (b) a non-adaptation control condition. The purpose was to test the hypothesis that the decreasing-loudness aftereffect may concern the sensory processing associated with dynamic localization. The hypothesis is based on two premises: (a) dynamic localization requires monaural sensory processing, and (b) sensory processing is reflected in spectral selectivity. Hence, the hypothesis would be supported if the monotic aftereffect were more spectrally dependent and stronger than the interotic aftereffect; A. H. Reinhardt-Rutland (1998) showed that the hypothesis is supported with regard to the related increasing-loudness aftereffect. Two listeners were exposed to a 1-kHz adapting stimulus. From responses of "growing softer" or "growing louder" to test stimuli changing in intensity, nulls were calculated; test carrier frequencies ranged from 0.5 kHz to 2 kHz. Confirming the hypothesis, the monotic aftereffect peaked at around the 1-kHz test carrier frequency. In contrast, the interotic aftereffect showed little evidence of spectrally dependent peaking. Except when test and adaptation carrier frequencies differed markedly, the interotic aftereffect was smaller than the monotic aftereffect.     

The minimum temporal thresholds for motion detection of grating patterns

The minimum temporal thresholds for absolute motion detection were measured for sinusoidal grating patterns in foveal vision. Test patterns of relatively low temporal frequencies and low velocities were examined. The thresholds clearly decreased with test velocities rather than with test temporal frequencies. Modified velocity-time reciprocity was observed (i.e. the relationship between test velocity and temporal thresholds was described by a simple equation including two constants which indicate temporal and spatial limits). The temporal constant was about 35 ms and the spatial constant was about 1 min of arc. These constants are thought to provide the basic constraints on motion detection.     

Effects of attentional modulation of a stationary surround in adaptation to motion

The effect of varying the spatial relationships between an adapt/test grating and a stationary surrounding reference grating, and their interaction with diversion of attention during adaptation, were investigated in two experiments on the movement aftereffect (MAE). In experiment 1, MAEs were found to increase as the separation between the surrounding grating and the adapt/test grating decreased, but not with the area of the adapt/test grating. Although diversion during adaptation (repeating changing digits at the fixation point) reduced MAE durations, its effects did not interact with any of the stimulus variables. In experiment 2, MAE durations increased as the outer dimensions of the reference grating were increased, and this effect did interact with diversion, so that the effects of diversion were smaller when the surround grating was larger. This suggests that diversion may be affecting the inputs to an opponent process in motion adaptation, with a smaller effect on the surrounds than on the centres of antagonistic motion-contrast detectors with large receptive fields. A third experiment showed that, although repeating the word 'zero' during adaptation reduced MAEs, this reduction was smaller than that from naming a changing sequence of digits (and not significantly different from that from simply observing the changing digits), suggesting that MAE reductions are not produced only, if at all, by putative movements of the head and eyes caused by speaking.     

Contour specificity of the McCollough effect

Subjective estimates of McCollough aftereffect strength are significantly reduced when certain spatial features of the line grating patterns are manipulated. Results are dependent upon whether the spatial parameters of the test or inspection patterns are altered. Changing the angular slant, contour sharpness, or contour completeness of the inspection gratings does not affect aftereffect strength, but changing the spatial frequency, contour sharpness, or contour completeness of the test gratings does. The implications of these results are discussed with regard to theories offered to explain the McCollough effect.     

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.     

Recovery from adaptation to moving gratings

Short-term adaptation to moving sinusoidal gratings results in a motion aftereffect which decays in time. The time decay of the motion aftereffect has been measured psychophysically, and it is found to depend on (i) the spontaneous recovery from the adapted state, and (ii) the contrast of the test grating. We have measured the decays for various test conditions. An extrapolation of the measurements allows us to obtain a decay which represents the time course of the spontaneous recovery of the direction-sensitive mechanisms.     

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.