What masks utrocular discrimination

Binocular fusion of luminance, color, motion and flicker--two eyes are worse than one

How much information is conserved, or discarded, as it travels through the visual system? A target (an oriented bar) was defined by dark grey spots embedded in light spots for the left eye, and by light grey spots embedded in dark spots for the right eye. With one eye open, the target bars were clearly visible, but with both eyes open the light and dark spots fused binocularly into medium grey and the target vanished. Results were similar for color; the target comprised greenish spots embedded in reddish spots for the left eye, and by reddish spots embedded in greenish spots for the right eye (somewhat like an Isihara color plate).

RESULT

The colored targets were invisible when both eyes were open but reappeared when one eye was closed. Small targets that moved in opposite directions in the two eyes were visible to each eye alone by common fate, but motion averaging made them disappear when both eyes were open.

CONCLUSION

Opposed retinal luminances or colors were averaged out by binocular fusion, but could be retrieved by a special afterimage technique in Experiment 6. Conversely, in Experiment 7 dichoptic target spots flickered in counterphase but background spots flickered in-phase to the two eyes.

RESULT

The targets were invisible monocularly but became visible as reduced-flicker when fused binocularly. We conclude that two eyes were worse than one eye when opposite colors or movements were fused (Experiments 1-6) but were better than one when binocular correlations could be extracted (Experiment 7). These experiments show how much of the visual information gets transmitted, gets discarded, can still be retrieved, or reaches conscious awareness.

Functional specialization in the lower and upper visual fields in humans: Its ecological origins and neurophysiological implications

Functional specialization in the lower and upper visual fields in humans is analyzed in relation to the origins of the primate visual system. Processing differences between the vertical hemifields are related to the distinction between near (peripersonal) and far (extrapersonal) space, which are biased toward the lower and upper visual fields, respectively. Nonlinear/global processing is required in the lower visual field in order to pergeive the optically degraded and diplopic images in near vision, whereas objects in far vision are searched for and recognized primarily using linear/local perceptual mechanisms. The functional differences between near and far visual space are correlated with their disproportionate representations in the dorsal and ventral divisions of visual association cortex, respectively, and in the magnocellular and parvocellular pathways that project to them. Advances in far visual capabilities and forelimb manipulatory skills may have led to a significant enhancement of these functional specializations.

Utrocular discrimination is not sufficient for utrocular identification

The distinction between reliability and validity is critical in examining utrocular identification. Four experiments demonstrated that two cues that lead to reliable discrimination do not lead to valid identification. Experiment 1 showed that, in the condition in which a stimulation of the right eye produced a visual direction toward the right and a stimulation of the left eye toward the left, there was a preponderance of correct responses. In the condition in which a stimulation of the right eye produced a visual direction toward the left and the left eye toward the right, there was a preponderance of incorrect responses. Experiment 2 showed that covariation of responses with visual direction decreased when feedback was provided because subjects sought other cues. Experiment 3, which included binocularly deficient subjects, showed that a feeling-in-the-eye is associated with the eye stimulated by a greater change in luminance rather than the eye stimulated by the target stimulus. When the luminance change was greater in the target eye, the feeling led to reliably correct responses, but when the luminance change was greater in the nontarget eye, it led to reliably incorrect responses. Experiment 4 indicated that the proportion of correct responses covaries with the degree of change in the luminance of the nontarget eye. The responses varied from reliably incorrect identifications, through unreliable identifications, to reliably correct identifications. These findings are consistent with the idea that stimulation of either eye is "projected" to the cyclopean eye.