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Visual Responses 

Visual Responses
Chapter:
Visual Responses
Author(s):

Riitta Hari

, and Aina Puce

DOI:
10.1093/med/9780190497774.003.0013
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date: 26 February 2021

This chapter introduces visual evoked responses. Transient VEPs are maximal across the posterior scalp and consist of three main deflections—N75, P100, and N135. Magnetic VEFs also show a prominent occipital response peaking at around 100 ms. Visual stimulation can include light flashes, pattern onset/offsets, pattern reversals and natural images. The extent and eccentricity of the visual stimulus can selectively encompass foveal or extrafoveal regions, or include quadrants, hemifield or the entire visual field. Stimulus attributes such as visual angle, spatial frequency, luminance and contrast greatly affect VEF and VEP amplitudes and latencies. Selective responses in the dorsal and ventral visual streams can be elicited with carefully chosen stimuli. Steady-state responses to periodically varying visual stimuli can be used to frequency-tag different aspects of the visual stimulus.

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