As your Fig3 C/D shows, no-TMS condition had somewhat lower level of correct responding for stack compared to frame stimuli. This may have made stack stimuli selectively more vulnerable for TMS effects with longer TMS delays.
Article Two critical periods in early visual cortex during figure–gr...
Good question. We didn't equalize performance in the no-TMS condition. Are you thinking of the explanation that more difficult conditions suffer more from TMS than easier conditions?
Dear Talis,
Thank you for your interesting question. No I did not equalize the frame vs stack correct perception rates as a baseline for the no-TMS condition. I think that stacks are indeed more susceptible to disruption by TMS, because they are more difficult to discriminate. This in fact might have increased the effect of TMS. However the finding of an intermediate time window without behavioral or electrophysiological effect of TMS indicates that there are two separate time windows in which areas V1/V2 are vulnerable for disruption during figure-ground segregation. In contrast, a widening of the window in which TMS had its effect would probably not have resulted in an intermediate time window without TMS effects. Let me know what you think!
Ilja and Martijn: thanks for replies. Let me comment. If in the no-TMS ("control") condition frame stimuli are better perceived than stack stimuli this may mean that the information the frames provide for the visual system is more robustly (eg, higher signal-to-noise ratio -- and here I mean not stimulus.noise, but brain-process noise) represented and as a consequence is stored better in sensory memory (e.g., 236-259 ms delay post stimulus). Consequently, TMS at that time has no strong effect. Whereas when stacks are a bit less well represented, they become more vulnerable to TMS at a later, sensory memory related (or sampling from memory related) epoch. I do not believe this is the case, but it may be worthy of controlling it experimentally: (1) equalize frame and stack, no-TMS, detection rates; (2) do the same experiment. (And yes, Martijn points out thoughtfully that an important and valuable aspect of this study is TWO separate time windows of the effects. Yet, maybe with less well represented frame stimulus in a control experiment 2 separate time windows emerge also for the frame stimuli.)
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