Effects of experimental scotomata on sequential pattern-onset, pattern-reversal and pattern-offset visual evoked potentials

Abstract

The effect of experimental scotomata on visual evoked potentials to half-field stimulation using sequential checkerboard onset, reversal and offset was investigated in 10 normal subjects to assess the relative sensitivity of the three stimulus modes, and the contributions of pathways subserving macular and paramacular parts of the visual field. Four scotoma sizes (0-1.5 degrees , 0 degrees - 2 degrees, 0 degrees -3 degrees and 0 degrees -4.5 degrees ) were used to mask the central part of the stimulus field (0 degrees -12 degrees ). Five check sizes (6', 12', 20', 50' and 80') were presented for each scotoma size. Peak-to-peak amplitudes and peak latencies of components on the ipsilateral and contralateral sides of the scalp to the stimulated half-field were measured. Scotoma size was highly significant in influencing component amplitude (p < 0.0001) and latency (p < 0.03) of all ipsilateral and contralateral onset components and all ipsilateral reversal and offset components. Components that were attenuated to the greatest extent with the smallest 0 degrees -1.5 degrees scotoma were the contralateral onset P105 and ipsilateral reversal P100 and N145. Onset CIII, reversal N80, and offset N85 and P110 only showed a significant attenuation after the use of scotomata of 0 degrees -3 degrees and larger. Our results show that scotoma size is a significant factor in influencing all the major visual evoked potential components, with the exception of reversal and offset contralateral potentials (N105 and N115), probably reflecting their paramacular origins. Reversal, ipsilateral P100 and N145, and onset, contralateral P105, appear to be predominantly of macular origin and the most sensitive potentials for detecting effects of small central scotomata.

Visual mismatch negativity to disappearing parts of objects and textures

“…Onset events usually elicit ERPs with larger amplitudes than offset events [19, 20]. We obtained similar results.…”

Effect of different stimulus configurations on the visual evoked potential (VEP)

“…Circular blank field sizes ranged from 1.25°to 15°, whereas square blank field sizes ranged from 2°to 24°, with a full complement of check sizes (6-80 min arc). Some of the studies found a ''nearly'' linear response profile [11][12][13]16], whereas others found a clear non-linear VEP response profile [14]. Thus, the findings of these earlier studies were equivocal.…”

“…Thus, the findings of these earlier studies were equivocal. Furthermore, only one study assessed the effect on response latency [16]; it remained constant for the range of field sizes tested. Again, and of critical importance, none of these studies assessed repeatability in their test populations.…”

Visual mismatch negativity to vanishing parts of objects in younger and older adults

“…It is important to note that deviant-related activity is superimposed on offset responses. Offset and onset ERPs are different from each other [ 26 ; 27 ], but offset responses are relatively infrequently investigated. Furthermore, the offset of the vanishing feature is followed by feature onset.…”