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Abstract:
Saccadic eye movements (SEMs) are the primary means of actively sampling the visual environment. The effect of saccadic eye movements on the neural processing of visual information has been characterized for retinotopic cortex [1,2], primarily in the forms of saccadic suppression [3]. Whereas previous studies have provided evidence for SEM-related activity in higher-order areas such as IT [4] and the hippocampus [5], we know of no investigation of neural activity in the STS, a region anatomically and functionally implicated in eye movements.
To address this issue, we analyzed local field potential (LFP) data recorded from the upper bank superior temporal sulcus (uSTS) of two awake rhesus macaques passively viewing images of faces and non-face objects. As expected, LFP phase and amplitude in different frequency bands were modulated relative to image onset (i.e. image-evoked responses). In addition, responses were modulated relative to fixation onset, and varied based on the delay between image onset and fixation onset, suggesting an interaction between visual-evoked and SEM-evoked responses. To determine whether ‘well-timed’ fixations would lead to greater phase-locking of the evoked response [1] we selected trials in which a fixation was made within 20 ms of image onset (quasi- ‘active vision' condition), and compared responses to trials in which no eye movements were made in the interval -150 to 200 ms relative to image onset ('passive vision' condition). Phase concentration was increased in the alpha and beta frequency bands around the onset time of image-evoked responses in the active compared to passive conditions. In addition, the mean phase across electrode sites became more consistent, resulting in a larger-amplitude population evoked response for active than passive conditions.
Our results demonstrate an interaction of sensory and saccadic signals in higher-order visual areas. The modulation observed is consistent with a role for active vision in reducing neural variability, enhancing signal transmission along visual pathways.
