The motion aftereffect reloaded

Abstract

The motion aftereffect is a robust illusion of visual motion resulting from exposure to a moving pattern. There is a widely accepted explanation of it in terms of changes in the response of cortical direction-selective neurons. Research has distinguished several variants of the effect. Converging recent evidence from different experimental techniques (psychophysics, single-unit recording, brain imaging, transcranial magnetic stimulation, visual evoked potentials and magnetoencephalography) reveals that adaptation is not confined to one or even two cortical areas, but occurs at multiple levels of processing involved in visual motion analysis. A tentative motion-processing framework is described, based on motion aftereffect research. Recent ideas on the function of adaptation see it as a form of gain control that maximises the efficiency of information transmission at multiple levels of the visual pathway.

Figure 1

Motion after-effect duration as a function of the temporal frequency of the test pattern (abscissa) and the speed of the adapting stimulus (different plot symbols). Results are shown for four subjects. For the slowest adapting speed (2.3 deg/sec, squares), MAE duration is maximal for stationary tests and absent at the highest test temporal frequency; for the fastest adapting speed (36.8 deg/sec, circles), the MAE is absent for stationary tests and maximal at the highest test temporal frequency (taken from [6]).

Figure 2

Contrast response functions of an MT neuron measured before adaptation (open symbols) and after adaptation (filled symbols). The inset in each graph shows the spatial arrangement of adapting and test stimuli in the cell’s receptive field (dotted lines). When adapting and test locations overlapped (A and D), the cell’s response was strongly reduced; when the adapting and test locations differed (B and C), response was largely unaffected by adaptation. (taken from [24]).

Figure 3

The posterior and anterior neural networks active during the perception of MAE; the connections between sites are derived from the correlation coefficients of the activation time courses. The lines join cortical sites which have cross correlations of at least 0.5. (Adapted from [36]).

Figure 4

Functional diagram relating the main stages of motion processing in the human brain to MAE adaptation sites. SMAEs are mediated by motion sensors that contribute to computation of ‘static’, while DMAEs are mediated by motion sensors that contribute to motion integration computations. Phantom MAEs involve sensors contributing to the computation of optic flow.