Effect of defocusing and of distracted attention upon recordings of the visual evoked potential

Abstract

Pattern reversal visual stimuli are used to evoke potentials (VEPs) for assessment of visual acuity and for localizing defects along the visual pathways. Our goal was to assess the importance of attention and defocusing to the recordings of pattern VEP. Forty-one volunteers with normal (6/6) corrected visual acuity participated in this study. Twenty-one were asked to defocus intentionally the visual stimulus (located 200 cm away) by fixating at a target 25 or 50 cm from the eye. Twenty other subjects performed auditory tasks to distract their attention from the visual stimulus. Pattern VEPs were elicited by different check sizes. The amplitude and time-to-peak of the P100 wave were measured. Intentional defocusing caused amplitude reduction and prolongation of the time-to-peak in young subjects (20-34 years old). With the smallest checks used (7.5') we could not record a reliable response from 43% of the young subjects (6 out of 14). In older patients (35-61 years old), intentional defocusing induced negligible effects on pattern VEPs regardless of check size. There were no effects of auditory distraction upon the pattern VEPs. Our data suggest that intentional defocusing can produce false positive results (reduced VEP with prolonged time-to-peak) only when small checks are used in young subjects. Divided attention has negligible effect on the recordings of pattern VEPs. With proper controls, the pattern VEP test can be used for objective assessment of visual function.

The Mouse Model of Down Syndrome Ts65Dn Presents Visual Deficits as Assessed by Pattern Visual Evoked Potentials

“…Additionally, because the VEPs in the present study were recorded from mice (which have non-foveate retinas) under anesthesia, the effect of attention and fixation in these experiments should have been negligible. Therefore, our results also help strengthen previous assessments in persons with DS, which have the inherent potential confounder of defocusing and of distracted attention, both of which can produce false positive results (reduced VEP with prolonged time-to-peak) in young subjects when small checks are used as pVEP stimuli 49.…”

Effect of test duration on the visual-evoked potential (VEP) and alpha-wave responses

“…As decreases in either or both would be expected to decrease the quality of the visual information, a decrease in VEP amplitude would be predicted [9]. However, the present results revealed the opposite: the VEP amplitude progressively increased with increasing test duration.…”

“…Across disease-free individuals in an age-matched sample, inter-individual VEP variability may result from differences in the anatomy of the primary visual cortex [5,6], influences of extrastriate cortices [7,8], gender [8] accommodative accuracy [9], and general and/or visual attention [9]. The latter two (accommodation and attention) may also change with time (i.e., test duration) [10-12], so this effect is important to consider as well: the VEP should be performed for no more, or less, time than necessary to obtain optimal responses.…”

Short-duration transient visual evoked potential for objective measurement of refractive errors

“…Blurred vision from uncorrected refractive error (RE) has been reported to decrease the VEP amplitude [2][3][4] and alter the latency (implicit time) of the VEP response [5,6]. An evoked potential measured using a checkerboard or other test field containing sharp contours and a lower check size is particularly sensitive to defocusing by uncorrected RE [7,8].…”