

A model is proposed suggesting how eye position-sensitive visual neurons might build up real-position cells in local networks within area PO (V6). In some cases, the receptive field did not move with gaze, remaining anchored to the same spatial location regardless of eye movements ('real-position cells'). In the great majority of visual neurons, the receptive field 'moved' with gaze according to eye displacements, remaining at the same retinotopic coordinates, as is usual for visual neurons. Moreover, the cortical distribution of eye position-sensitive neurons was quite uniform all over the cortical region studied, suggesting the absence of segregation for this property within area PO (V6). The spatial distribution of fixation point locations evoking peak activity in the eye position-sensitive population did not show any evident laterality effect, or significant top/bottom asymmetry. Eye position fields and/or gain fields were different from cell to cell, going from large and quite planar fields up to peak-shaped fields localized in more or less restricted regions of the animal's field of view. About 48% of visual and 32% of non-visual neurons showed eye position-related activity in total darkness, while in approximately 61% of visual response was modulated by eye position in the orbit. Both visual and non-visual neurons were found. Animals sat in a primate chair in front of a large screen, and fixated a small spot of light projected in different screen locations while the activity of single neurons was extracellularly recorded. Experiments were carried out on three awake macaque monkeys. The aim of this work was to study the effect of eye position on the activity of neurons of area PO (V6), a cortical region located in the most posterior part of the superior parietal lobule. The results are discussed with reference to clinical application and spatial dis- orientation in aviation. Performing a difficult subtraction task with eyes closed may afford a decrease in dual-task interference since similar brain areas, particularly the parietal region, are involved in both tasks. We conclude that sensory processing load with eyes closed is lower than eyes open in the dark, thereby allowing cognitive performance to proceed more efficiently. Accuracy was not affected among the visual and surface conditions. Subtraction speed under the fixed support surface condition was similar among all the conditions but was faster with eyes closed during the sway-ref- erenced support surface condition. Analyses of the cognitive performance also revealed different un- derlying neural mechanisms of the experimental con- ditions. The second component was the effect of task difficulty in which balance control in the sway-ref- erenced condition was worse compared to fixed support during eye closure or eyes open in the dark.

Balance control during eye closure and eyes open in the dark were found to be similar but poorer than baseline condition (eyes open under typical lighting). The first component came from the visuospatial factor. Peak-to-peak anteroposterior sway performance revealed two dissociated components of the treatment effects. A variety of cognitive (subtracting backwards by seven as quickly and accurately as possible) and sup- port surface (fixed versus sway-referenced) conditions were used to probe the neural mechanisms underlying the sensory organization processes in healthy young adults. On the other hand, when the eyes are closed, the visual system does not signal incongruent information with which the brain must compare the other sensory sys- tems. We hypothesized that keeping one’s balance with eyes open in the dark is different and more difficult than eyes closed because the brain continues to process visual inputs in the dark when the eyes are open.
