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.

The Role of Intervening Patterns in the Storage of the Movement Aftereffect

Wohlgemuth, having measured the duration of the motion aftereffect (MAE), instructed subjects to close their eyes immediately after adaptation for a period of time longer than the MAE. Upon opening their eyes the subjects reported a residual effect, albeit somewhat shorter than the original effect. Thus the decay of the aftereffect appeared to have been retarded by the period of darkness. This effect is known as ‘storage’ and poses a problem for any model of the MAE based on the fatiguing of direction-selective units in the visual pathway. A reexamination is made of storage of the MAE, again concentrating on the intervening stimulation between movement adaptation and aftereffect test. The results suggest that the nature of the intervening pattern between adaptation and test conditions is remarkably unimportant. A total of 11 different storage patterns were examined after adaptation to high-contrast drifting horizontal sinewave gratings. For 10 of these patterns large and robust storage effects were found. The exception occurred when the spatial pattern of the storage stimulus was identical to the adaptation and test stimuli. It is proposed that storage cannot be understood in terms of a simple fatigue model of the MAE and that one component of the effect may share similarities with contingent aftereffects.

Ensemble Models of the Movement Aftereffect and the Influence of Eccentricity

Moving random-pixel arrays (RPAs) were used to study the movement aftereffect (MAE) for translational texture motion and to quantify the contribution of RPA-sensitive motion sensors to the MAE as a function of eccentricity. Size-scaled patterns were used to make a fair comparison across eccentricities. At the upper end of the velocity range it was found, for all eccentricities, that motion sensors tuned to velocities exceeding about 10–20 deg s−1 do not contribute to the translational MAE, even though they do contribute to motion perception. As a consequence the subpopulation of local motion sensors that contributes to the MAE shrinks with eccentricity, because there are fewer low-velocity-tuned and more high-velocity-tuned motion sensors for increasing eccentricity. Thus there is a quantitative, but not a qualitative, difference between the MAEs generated at different eccentricities.

Spatial Integration in Coherent Motion Detection and in the Movement Aftereffect

Sensitivity characteristics and spatial integration properties of the motion-detection system are compared with those of the system responsible for the movement aftereffect (MAE), elicited by the same stimulus. This provides new information about the mechanisms involved in MAE generation. A screen was divided into a chequerboard where the squares were filled with random-pixel arrays moving in opposite directions. Changing the size of the squares produced drastic changes in the percept during the adaptation phase and in the MAE during the test phase. One striking new phenomenon that is described is ‘structure from MAE’. The results indicate that the receptive fields of units involved in eliciting the MAE are larger than the receptive-field sizes of units involved in detection and segregation of motion components in the stimulus. Furthermore, the results suggest that the receptive fields contributing to the MAE are involved in complex interactions in which different local motion directions are integrated in pattern-specific ways.

The Duration of the Movement Aftereffect as an Index of Psychiatric Illness

The duration of the movement aftereffect (MAE) has sometimes been used to make inferences about the subject's state (for example, their level of arousal). Some studies are reviewed in which visual aftereffects (including the MAE) were measured in schizophrenia, with inconsistent results. Some relevant psychopharmacological and neurological evidence is considered. It is concluded that: (i) Differences in the clinical status of the schizophrenic subjects and whether they were receiving medication, but not the method used to measure aftereffects, may underlie the interstudy disagreements. (ii) The effect of schizophrenia is to increase MAE duration, and this is not due to some peripheral artefact. (iii) Longer MAEs in the illness could result from enhanced neurally signalled contrast and/or from the increased adaptability of cortical neurons.