Abstract
Two visual signals appearing simultaneously are detected more rapidly than either signal appearing alone. Part of this redundant target effect (RTE) can be attributed to neural summation that has been proposed to occur in the superior colliculus (SC). We report direct evidence in two neurological patients for neural summation in the SC, and that it is mediated by afferent visual information transmitted through its brachium. The RTE was abolished in one patient with a hemorrhage involving the right posterior thalamus that damaged part of the SC and that disrupted its brachium; and in another patient in whom the SC appeared intact but deafferented due to traumatic avulsion of its brachium. In addition reaction time for unilateral targets in the contralesional field was slowed in both patients, providing the first evidence that visual afferents to the SC contribute to the efficiency of target detection.
Highlights
Two visual signals appearing simultaneously are detected more rapidly than either signal appearing alone (Hershenson, 1962; Raab, 1962)
A posterior thalamic hemorrhage 3 years earlier destroyed the medial pulvinar, ventro-lateral thalamic nuclei and the posterior limb of the internal capsule with damage extending into the dorsal midbrain including the pretectum and rostral superior colliculus (SC) (Figure 1) Probabilistic DTI tractography (Behrens et al, 2003, Behrens et al, 2007) confirmed that the lesion destroyed the brachium of the SC (Figure 2)
Simple reaction time (RT) were measured to detect single targets in either contralesional or ipsilesional field, and bilateral targets, in two patients in whom the brachium of the SC was damaged in one hemisphere
Summary
Two visual signals appearing simultaneously are detected more rapidly than either signal appearing alone (Hershenson, 1962; Raab, 1962) Part of this redundant target effect (RTE) can be accounted for stochastically by a ‘horse-race’ model. In hemispherectomy patients a redundant target in the blind field generates a RTE, the RTE is augmented when the redundant stimulus completes a gestalt pattern (Georgy et al, 2016). These observations in Frontiers in Systems Neuroscience | www.frontiersin.org van Koningsbruggen et al
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