Interaction between different types of visual information Big question: the ‘binding problem’ (how are separate neural representations re-combined?) Smaller question of this paper: where (not how or why) do motion and position information interact?

Motion aftereffect (‘static’ MAE) Stare at moving stripes/dots for a while (adapt) Inspect a stationary version of the adapting pattern Old story: a sensation of motion without position shift New story: a sensation of motion + apparent shift of position (in the direction of the MAE)

Site of interaction? Previous suggestion: In V1 or V2, via connections from V5/MT (Nishida and Johnston, 1999), because small RFs in V1 would give good position sensitivity. Authors suggest it all happens in V5 (more parsimonious than backwards projections from V5 to V1)

Overview of experiment Perceived misalignment of static test stimuli produced by prior adaptation to motion (via MAE) Attempt to disrupt this misalignment by TMS during perception of the test field TMS applied to V1 or V5 Also compared with effects of TMS to V5 after adapting to counter-phased gratings (don’t produce misalignment in test field) If TMS disrupts perceived misalignment, that area is involved in integration of motion and position

Experimental design

Author’s conclusion TMS affects perceived misalignment when applied to V5, but not to V1 Integration of motion and position information occurs in V5, not V1

Problem (1) What is TMS doing? Authors suppose it in affecting integration in V5 But it may be affecting motion signal in V5 (which affects what goes back down to V1) and adding a little noise to the integrated information in V1 We are not told how the measurements were made (‘via standard psychophysical procedures’)

Problem (2) How can we be sure that TMS affected relevant processing in V1? Authors say: In two Ss, coil position was localised by structural MRI. So TMS was applied to V1, but its effects uncertain In other 2 Ss, ‘use of stationary and moving phosphenes established locus of V1 and V5’ Web address for more details no longer exists

Problem (2 cont.) Missing condition?: Apply TMS to V1 and V5 during adaptation (would show whether relevant motion-sensitive neurons in V1 as well as V5 are affected by TMS) Does TMS have any effects in V1? We need to know this in order to interpret the lack of effect in the alignment task

Problem (3) How does TMS affect vision? If you hit V5, motion-sensitive neurons are presumably affected, but how? Temporary reduction in output? How do the Gabor test patches appear with V1 and V5 TMS? Distorted? Normal? Why is only motion apparently affected by TMS?

My conclusion TMS affects V5, but it’s not clear how Nishida and Johnston’s idea still alive – if the TMS to V5 disrupts motion signals down to V1 TMS to V1 need not affect integrated signals RAE panel should look hard at papers in Current Biology