Christine L McKay

Visual evoked responses elicited by rapid stimulation

Abstract An assessment of the technique of eliciting VERs with rapid rates of stimulation has revealed that differences in evoked response due to stimulus parameters may be minimized under these conditions. The probable reason is that addition of ongoing activity from one flash to that elicited by another occurs; this addition can obscure or enhance wave form differences present in the complete evoked response. A comparison of visual-evoked responses (VERs) to rapid flash rates which were empirically determined with VERs synthesized from a linear addition of the first two segments of the complete evoked response reveals a rather remarkable agreement in most cases. On the other hand, some failures to predict empirical data in this manner to occur. These failures are not due to temporal variations and their etiology is unknown at this time. Until the electrogenesis of the VER is understood, we conclude the use of both a fast and a slow rate to obtain VERs is a good methodological technique for studying brain functioning.

Test of color-defective vision using the visual evoked response*†

This paper describes a new technique for detecting color-defective individuals, based upon the isolation of a pattern response from the visual evoked response. Specifically designed targets were produced from equal-luminance hues that lie on the confusion lines of deuteranopes, protanopes, and tritanopes. Sixteen color normals, eight deuteranopes, eight protanopes, and one tritanope were tested with these targets. The results showed that color normals give a pattern response to patterns formed of hue differences only; this response is similar to that produced by luminance differences. Color-defective individuals, on the other hand, give no pattern response to targets formed of hues that they cannot discriminate, although they give pattern responses for luminance differences.

Techniques for analysing differences in vers: Colored and patterned stimuli

Abstract Statistical and experimental techniques for analysis of visual evoked responses (VERs) to colored and patterned stimuli were compared. Statistical analysis of the amplitudes and latencies of components was effective in evaluating subtle differsences among VERs, such as different responses to hues by color normal and color defective individuals. For gross changes in VER, as an found Drift patterned versos blank fields, an experimental technique was preferable. This consists of summing the responses to one stimulus and subtracting the same number to another. A distinct pattern element was extracted by this technique which was similar for all colors.

Vision through Various Scuba Facemasks

The visual performance using five commercially avaible facemasks was compared. Measurements were made of visual fields, visual acuity, stereoacuity, hand-eye coordination, accuracy of distance estimates, and accuracy of size estimates at both near and far distances. In addition, the optical properties of the masks were measured and the susceptibility of each mask to fogging was tested. There were significant differences among the masks for every visual process tested. Some masks were superior for one purpose and inferior for another purpose. For example, the mask which had lenses designed to compensate for the optical distortions found under water improved size and distance estimates and hand-eye coordination, but degraded acuity and stereoacuity. The results were not expplained on the basis of differential susceptibility to fogging.