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PubMed1993

Apparent motion perception: the contribution of the binocular and monocular systems. An improved test based on motion aftereffects.

Research concerning the perception of apparent motion is not easy to conduct: it is hard to obtain quantitative results that can be easily interpreted. A solution to this problem is the use of motion aftereffects (MAEs). Adapting subjects to a specific type of motion leads to apparent motion in the opposite direction when the stimulus is removed. However, subjects are aware of the change in stimulus conditions. A new dynamic test stimulus is proposed in order to avoid artefacts introduced by the awareness of the conditions by the subject. A model, derived from earlier observations, is described which includes contributions from monocular and binocular systems. Results from an experiment in which the dynamic test stimulus was used show that they do not necessarily reproduce the results obtained with a static test stimulus. Central monocular systems are added to the model to account for this discrepancy. The 'pooling hypothesis', which states that the MAE is a weighted mean of the processes involved, permits the estimation of the weights of the individual subsystems. The results of the experiments are explained in terms of this hypothesis by the new model.

Adaptation, Ocular↗

PubMed2006

Slant perception, and its voluntary control, do not govern the slant aftereffect: multiple slant signals adapt independently.

Although it is known that high-level spatial attention affects adaptation for a variety of stimulus features (including binocular disparity), the influence of voluntary attentional control-and the associated awareness-on adaptation has remained unexplored. We developed an ambiguous surface slant adaptation stimulus with conflicting monocular and binocular slant signals that instigated two mutually exclusive surface percepts with opposite slants. Using intermittent stimulus removal, subjects were able to voluntarily select one of the two rivaling slant percepts for extended adaptation periods, enabling us to dissociate slant adaptation due to awareness from stimulus-induced slant adaptation. We found that slant aftereffects (SAE) for monocular and binocular test patterns had opposite signs when measured simultaneously. There was no significant influence of voluntarily controlled perceptual state during adaptation on SAEs of monocular or binocular signals. In addition, the magnitude of the binocular SAE did not correlate with the magnitude of perceived slant. Using adaptation to one slant cue, and testing with the other cue, we demonstrated that multiple slant signals adapt independently. We conclude that slant adaptation occurs before the level of slant awareness. Our findings place the site of stereoscopic slant adaptation after disparity and eye posture are interpreted for slant [as demonstrated by Berends et al. (Berends, E. M., Liu, B., & Schor, C. M. (2005). Stereo-slant adaptation is high level and does not involve disparity coding. Journal of Vision 5 (1), 71-80), using that disparity scales with distance], but before other slant signals are integrated for the resulting awareness of the presented slant stimulus.

Adaptation, Physiological↗

PubMed1982

Binocular adaptation that cannot be measured monocularly.

The tilt aftereffect (TAE) is used to demonstrate the existence of a purely binocular process in human vision. A purely binocular process is a process that can be activated only by matched inputs to the two eyes. It is insensitive to monocular stimulation. The TAE can be produced by exposure to a bipartite field with the top tilted to the left of vertical, the bottom to the right. After such adaptation a pair of colinear lines appears bent in the opposite direction. A cyclopean random-dot stereogram can be used as an adapting stimulus. It produces a 2 degree TAE when a cyclopean test stimulus is used and a 1 degree TAE when a binocular but noncyclopean test stimulus is used. If the same noncyclopean pattern is viewed monocularly, no TAE is measurable. The TAE does not transfer from cyclopean adaptation to monocular testing. Apparently, cyclopean stimuli activate a 'purely binocular process' that cannot be activated by either eye alone.

Adaptation, Ocular↗

PubMed1997

Contrast dependencies of two types of motion aftereffect.

We examined the effects of adaptation and test contrasts on the duration of two types of motion aftereffect (MAE) that presumably reveal different levels of motion processing: MAE with a static test stimulus (static MAE), and that with a counterphasing test stimulus (flicker MAE). MAE duration increased with increasing adaptation contrast. When the test contrast was low, it increased rapidly, and saturated at a low adaptation contrast. When the test contrast was high, however, it gradually increased over a wide range of adaptation contrasts. These complex effects of stimulus contrasts could be well described by a dependency on adaptation contrast normalized by test contrast on a logarithmic axis. Little difference was found between the results for two types of MAE. The interaction between adaptation and test contrasts leads us to reject the idea that the shape of adaptation contrast dependency of MAE duration reflects that of the sensitivity function of motion detecting mechanisms. The results also suggest a functional similarity between the processes underlying static and flicker MAEs with regard to their responses to contrasts.

Adaptation, Physiological↗

PubMed1992

Positive motion after-effect induced by bandpass-filtered random-dot kinematograms.

Using spatially filtered random-dot kinematograms (RDK) with a 1 octave bandwidth, the duration and direction of motion aftereffect (MAE) were measured while varying step displacement, and the results were compared to those for motion direction discrimination. We found that MAE and motion discrimination show quite different dependencies on displacement. At displacements around 0.5 cycles of the lowest frequency, while motion discrimination was still almost perfect, normal MAE vanished and MAE in the same direction as that of the adapting stimuli, which we name "positive MAE", was observed. Similar results were obtained for both 1- and 2-dimensional filtered patterns. A theoretical examination based on the Fourier components of the stimuli showed that the displacement dependency of MAE is predictable in terms of adaptation of first-order detectors, but that of motion discrimination is not. The present results indicate that direction perception and MAE for bandpass RDKs are mediated at least partially by separate mechanisms, and that direction perception at larger displacements is mediated by the second-order mechanism which detects movement of contrast modulation in the image.

Adaptation, Ocular↗

PubMed2000

The spatial spread of attentional modulation of the motion aftereffect.

The spatial spread of attentional modulation of selective adaptation was investigated in four experiments in which the duration of the movement aftereffect (MAE) was measured with and without processing of intermittently changing digits at the fixation point. In the first experiment, the effects of diverting attention on MAE duration were found to reduce as the distance between the fixation digits and the inner edge of the surrounding adapt/test grating was increased. A second experiment suggested that eye movements were unlikely to underlie the attentional effects. In experiment 3, the attentional effect stayed constant as the outer diameter of the adapt/test gratings was increased. In experiment 4 (as in experiment 1) the modulatory effects of attention were larger the closer the adapt/test gratings were to the locus of attention, when the area of the grating was held constant but its eccentricity varied. In experiments 1 and 4, an intermittently changing fixation digit was found to reduce MAE durations more than an unchanging digit, even when subjects were not required to process it, suggesting that exogenous as well as endogenous attentional processes modulate early motion processing.

Attention↗

PubMed2001

Differential effect of attention to translation and expansion on motion aftereffects (MAE).

Recent fMRI findings have shown that selective attention to translating dots enhances V1 and MT complex activity whereas attention to expansion enhances MT complex activity rather than V1 (Watanabe et al., Proceedings of the National Academy of Sciences of the USA, (1998a) 95(19), 11489-11492). In order to clarify whether or not attention actually enhances the neural mechanism for the attended motion direction(s), we took advantage of the motion aftereffect (MAE), using superimposed groups of translating and expanding dots as the adaptation stimulus. During the adaptation stage, the subject was instructed to direct attention to one-way translation, expansion, or no particular motion or location, while gazing at the fixation point. The strength of the MAE in the attended monocular condition was greater than the sum of the unattended monocular MAE and the attended binocular MAE. In another experiment the monocular and binocular components showed linear additivity. These results suggest that attention enhances the monocular mechanism for the attended translational direction and that bottom-up monocular signals and top-down attentional signals simply add linearly. In contrast, no significant monocular contribution was found for attention to expansion. This is not only in accord with previous fMRI findings (Watanabe et al., 1998a), but also supports the thesis that attention to translation or expansion enhances the activation of the mechanism for the attended motion, rather than simply increasing arousal as a result of a heavier task load.

Adult↗

PubMed2000

Tilt dependency of slant aftereffect.

Slant aftereffect (SAE), the negative aftereffect of slant induced after prolonged observation of a surface, is considered as evidence that slant is encoded in the visual system. Because slant and tilt are mathematically independent dimensions, Stevens (Stevens, K. A. (1983a). Biological Cybernetics, 46, 183-195) assumed that slant and tilt are processed independently in the visual system. To confirm this assumption, we investigated whether SAE is induced independently of the difference in tilt between the adapting and test stimuli. The stimuli were displayed by simulating the motion disparity of rotating disks. After adaptation to a surface of 60 degrees slant, the subjective 0 degree slants of the test stimulus were measured with the tilt differences of 0, 45, 90, 135 and 180 degrees. The magnitude of SAE was greatest when the tilt difference was zero, and decreased with increasing tilt difference. The results suggest that slant and tilt are not processed independently in the visual system and that the slant detector in the visual system is sensitive not only to slant but also to tilt.

Computer Simulation↗

PubMed2003

Influence of viewing distance on aftereffects of moving random pixel arrays.

Viewing-distance invariance of visual perception has evolutionary advantages, but it is of necessity limited by spatial and temporal resolution. Even within these resolution limits viewing-distance invariance might not be perfect or even good, but there are remarkably few studies of its precise limits. Here we ask to what extent viewing-distance invariance holds for motion aftereffects (MAEs). There are (at least) two different MAEs: one can be seen on a static test pattern (sMAE) and is tuned to low speeds, the other only becomes manifest on a dynamic noise test stimulus (dMAE) and is sensitive to higher adaptation speeds. We show that each of these MAEs has a limited viewing-distance invariance, the dMAE only for higher screen-speeds and the sMAE only for lower screen-speeds. In both cases upper angular-speed limits shift to higher values for smaller viewing-distances (lower spatial frequencies, larger fields). This upper limit is constant, independent of viewing distance, if expressed in terms of screen-speed. On the other hand the lower speed limit is fixed in angular-speed and variable in screen-speed terms. Explanations for these findings are provided. We show that there is no fixed optimum viewing-distance or optimum angular stimulus-size for either of the two MAEs.

Computer Graphics↗

PubMed2000

A hierarchical structure of motion system revealed by interocular transfer of flicker motion aftereffects.

Interocular transfer of the motion aftereffect (MAE) has been extensively investigated for the purpose of analysing the binocularity of the underlying motion mechanism. Previous studies unanimously reported that the transfer of the classical static MAE is partial, but there is a controversy as to whether the transfer of the flicker MAE (MAE measured using counterphase gratings) is partial or perfect. To gain insight into the discrepancy between studies, we investigated whether the interocular transfer of the flicker MAE is influenced by the MAE measurement method, retinal eccentricity and attention. Our results showed that the transfer was perfect or nearly so when the MAE duration was measured in the central visual field with observers paying attention to the adaptation stimulus, but the transfer was partial when the MAE nulling strength was measured, when the MAE duration was measured in the peripheral visual field, or when the observers' attention was distracted by a secondary task. These results not only resolve discrepancies between previous studies, but also suggest that the flicker MAE reflects adaptation at multiple stages in the hierarchical architecture of motion processing.

Adaptation, Physiological↗

PubMed1994

Perception of motion in depth from luminous rotating spirals: directional asymmetries during and after rotation.

Motion aftereffect (MAE) following spiral rotation is often asymmetrical: centrifugal MAE exceeds centripetal MAE. Pronounced MAE asymmetry has been reported for conditions--especially with a minimal background pattern--promoting perception of motion in depth. Such conditions are predicted to elicit motion asymmetry during adaptation. In the present study observers viewed luminous spirals monocularly in the dark; they timed, and scaled for convincingness, motion in depth during and after rotation. Motion in depth during rotation was often almost continuous, but recession was more convincing than was approach. Approaching MAE lasted longer and was more convincing than was receding MAE: the duration difference was more pronounced than has been found in other MAE studies, corroborating the link between MAE asymmetry and motion in depth. A possible line of explanation resides in comparing spiral motion in depth with real motion in depth of objects: in particular, the rapid visual change and collision with the observer that characterises real approach of an object is lacking in spiral approach. Interspecies differences for 'looming' and MAE are discussed.

Adult↗

PubMed2002

[Effect of central and surrounding gratings of test stimulus on appearance of motion aftereffect].

We conducted three experiments to examine the effect of spatial arrangement of test stimulus on the motion aftereffect (MAE). The adaptation and test stimuli were presented to subjects successively. Each adaptation stimulus consisted of a set of three gratings; a central stationary grating was located between the two surrounding gratings, one above and the other below respectively, which were arranged to move leftward for two minutes. The location and/or the shape of the test stimulus were varied to examine the effects of the spatial arrangement. The first and second experiments revealed that the MAE lasted longer when the surrounding gratings for the test were superimposed on those for the adaptation than when they were not superimposed. Further, the results of both experiments showed that the duration was not affected by the distance between the central grating and surrounding one. The results of the third experiment showed that the MAE lasted longer when the central grating for the test was identical with that for the adaptation than when not, and that the surrounding for the test need not to be identical with that for the adaptation. These results support Wade's hypothesis for explaining how MAE occurs.

Figural Aftereffect↗

PubMed1999

Motion aftereffect of combined first-order and second-order motion.

When, after prolonged viewing of a moving stimulus, a stationary (test) pattern is presented to an observer, this results in an illusory movement in the direction opposite to the adapting motion. Typically, this motion aftereffect (MAE) does not occur after adaptation to a second-order motion stimulus (i.e. an equiluminous stimulus where the movement is defined by a contrast or texture border, not by a luminance border). However, a MAE of second-order motion is perceived when, instead of a static test pattern, a dynamic test pattern is used. Here, we investigate whether a second-order motion stimulus does affect the MAE on a static test pattern (sMAE), when second-order motion is presented in combination with first-order motion during adaptation. The results show that this is indeed the case. Although the second-order motion stimulus is too weak to produce a convincing sMAE on its own, its influence on the sMAE is of equal strength to that of the first-order motion component, when they are adapted to simultaneously. The results suggest that the perceptual appearance of the sMAE originates from the site where first-order and second-order motion are integrated.

Contrast Sensitivity↗

PubMed1993

Linear and rotation motion aftereffects as a function of inspection duration.

Subjects rated the strength of linear and rotary motion aftereffects (MAEs) on an eleven point scale. Inspection durations ranged from 30 to 180 sec in 30 sec steps. In Expt 1, trials using a single inspection duration were spaced at least 22 hr apart to minimize the possibility of interactions between adapting stimuli and long lasting aftereffects. In Expt 2, a counterbalanced sequence of inspection durations was completed in a single session. Total duration of the MAE and durations of the decay phase and tail were measured directly. The decay time constant (DTC), the time it takes for rated strength of the MAE to drop to 1/e of its initial value, was calculated from a line fit to a semilog plot of the ratings during the decay phase. The DTC is inversely related to the decay rate which is indexed by the slope of this line. In both experiments, the duration and DTC increased, and decay rate decreased, with increasing inspection duration for both rotary and linear MAEs. This finding replicates the results for linear MAEs and extends them to rotation MAEs. There were no discernible differences between the two types of MAEs. When the trials were spaced, the total duration increased with the square root of inspection duration. The DTC did not follow the square root rule over the entire range but appeared to approximate it for inspection durations of 90 sec and above. When trials were massed, the square root rule did not appear to apply at all.

Adaptation, Ocular↗

PubMed1982

Thresholds for seeing visual phantoms and moving gratings.

Moving visual phantoms look like real gratings and generate movement aftereffects as do real gratings. Three experiments have been carried out to test whether phantoms resemble real gratings in other ways. Changes in the spatiotemporal frequency of an inducing grating effect the minimum contrast at which it will induce phantoms, but only insofar as the changes affect the visibility of the inducing gratings. Changes in the areal extent of the inducing grating and in the extent of the gap across which phantoms must be induced alter the visibility of the phantoms but, again, only to the extent that the changes affect the visibility of the inducing gratings themselves. Phantoms induced by high-contrast gratings may be cancelled by gratings of near-threshold contrast when the latter are presented 180 degrees out of phase with the inducing gratings. It is concluded that the appearance of phantoms is governed solely by the detectability of their inducing gratings, but that the effects of phantoms on pattern-sensitive channels are not the same as are the effects of real gratings. The pattern characteristics of phantoms thus do not represent a spread of energy from inducing to phantom regions of visual space or their neural representations.

Figural Aftereffect↗

PubMed2002

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.

Computer Graphics↗

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↗

PubMed2006

The direction aftereffect is driven by adaptation of local motion detectors.

The processing of motion information by the visual system can be decomposed into two general stages; point-by-point local motion extraction, followed by global motion extraction through the pooling of the local motion signals. The direction aftereffect (DAE) is a well known phenomenon in which prior adaptation to a unidirectional moving pattern results in an exaggerated perceived direction difference between the adapted direction and a subsequently viewed stimulus moving in a different direction. The experiments in this paper sought to identify where the adaptation underlying the DAE occurs within the motion processing hierarchy. We found that the DAE exhibits interocular transfer, thus demonstrating that the underlying adapted neural mechanisms are binocularly driven and must, therefore, reside in the visual cortex. The remaining experiments measured the speed tuning of the DAE, and used the derived function to test a number of local and global models of the phenomenon. Our data provide compelling evidence that the DAE is driven by the adaptation of motion-sensitive neurons at the local-processing stage of motion encoding. This is in contrast to earlier research showing that direction repulsion, which can be viewed as a simultaneous presentation counterpart to the DAE, is a global motion process. This leads us to conclude that the DAE and direction repulsion reflect interactions between motion-sensitive neural mechanisms at different levels of the motion-processing hierarchy.

Adaptation, Ocular↗