Extended Data Fig. 3: Stability and separability of foveolar loci despite different distributions of eye movements.

With (A) poorer (85% within 1°) and (B) better (95% within 1°) eye fixation behavior, activations on the cortex remain very similar (see circles). We considered the possibility that the spatial distribution of eye movements leads to stimulation by the edges of the spot that activate the loci that we interpret as the foveolar centers. We show here that our data preclude this possibility. First, this scenario predicts that if, the eye movement distribution is larger, then the edges should activate more peripheral loci on the cortex. However, in two sessions in which the monkey exhibited (A) poorer (85% within 1°) and (B) better (95% within 1°) eye fixation behavior, the activations on the cortex remain very similar (see circles marking foveolar loci). Second, it predicts that a larger (for example 0.8°) would activate more peripheral locations on the cortex than a smaller (for example 0.4°) stimulus. However, as shown in Fig. 3 and Extended Data Fig. 1 of the manuscript, the foveolar loci are stable across 3 spots sizes, in each of 2 monkeys. Finally, if the responses were due to edge effects from eye movements, the result would not be two focal and punctate activations, but a continuous activation zone elicited by the many directions of eye movements. Logically, blurring would only serve to make the loci larger and less separable, thereby indicating our results are an overestimate of foveolar activation size, which would mean the actual size of foveolar loci are even smaller and even more distinguishable. Thus, our results are not an artifact of eye movements.

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