Novel effects of adaptation in area MT

Adam Kohn and J. Anthony Movshon


We have evaluated the effect of prolonged (40 s) adaptation on the direction tuning of macaque area MT/V5 neurons using drifting sine wave gratings. Preferred adaptation consistently caused a narrowing of direction tuning, because the response in the adapted direction was reduced less strongly than that in other nearby directions. A similar phenomenon was observed following adaptation at near-preferred ('flank') directions, with the consequence that the direction tuning of MT cells was attracted toward the adapted direction. Flank adaptation of complex cells in primary visual cortex (V1) did not cause an attractive shift in direction tuning. Finally, null adaptation often caused an increase in direction tuning bandwidth in MT neurons, but did not alter their preferred direction or responsivity. We suggest that these novel effects of adaptation on direction tuning in area MT are consistent with perceptual aftereffects and provide functional benefits not afforded by the repulsive shifts in tuning typically observed in V1.