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Florian Ostendorf, Daniela Liebermann, Christoph Ploner; Conscious perception of intrasaccadic displacements is deficient in a patient with a focal thalamic lesion. Journal of Vision 2009;9(8):374. doi: https://doi.org/10.1167/9.8.374.
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In everyday life, we continuously sample our visual environment by rapid sequences of saccadic eye movements and intervening brief fixations. For the successful integration of visual information into a coherent scene representation the brain needs to deal with these constant self-induced displacements of the visual scene on our retinae. An internal “forward” model (Miall and Wolpert, 1996; Sommer and Wurtz, 2008) may decisively contribute to the latter problem: The brain may use an internal monitoring signal associated with the oculomotor command to predict the visual consequences of the corresponding saccadic eye movement and compare this prediction with the actual postsaccadic visual input.
Recent neurophysiological studies in primates identified one candidate pathway for an internal monitoring signal that ascends from the superior colliculus to the frontal cortex, relayed by medial parts of the thalamus (Sommer and Wurtz, 2002). Whereas its pharmacological inactivation suggests a role of this pathway for movement planning, a more general role in perceptual-motor integration can be expected. Here, we studied the dynamics of transsaccadic space perception in young patients with focal thalamic lesions. We utilize the phenomenon of “saccadic suppression of displacement” (SSD), i.e., the observation of elevated thresholds for the conscious detection of location changes during saccadic eye movements.
In this task, a patient with a right medio-dorsal thalamic lesion exhibited markedly elevated thresholds of conscious displacement detection for saccades directed in the hemi-field ipsilateral to lesion side. By contrast, corrective saccades were properly performed to the intrasaccadic target step. Our finding highlights the relevance of internal monitoring signals for perceptual-motor integration and conscious visual perception in general. Internal monitoring signals may be critically important for the correct attribution of self-induced versus externally imposed changes in the continuous flow of our sensory experiences.
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