Intra-saccadic displacement sensitivity after a lesion to the posterior parietal cortex

Visual perception is introspectively stable and continuous across eye movements. It has
been hypothesized that displacements in retinal input caused by eye movements can be
dissociated from displacements in the external world using extra-retinal information, such
as a corollary discharge from the oculomotor system. The extra-retinal information can
inform the visual system about an upcoming eye movement and accompanying displacements in retinal input. The parietal cortex has been hypothesized to be critically
involved in integrating retinal and extra-retinal information. Two tasks have been widely
used to assess the quality of this integration: double-step saccades and intra-saccadic
displacements. Double-step saccades performed by patients with parietal cortex lesions
seemed to show hypometric second saccades. However, recently idea has been refuted by
demonstrating that patients with very similar lesions were able to perform the double step
saccades, albeit taking multiple saccades to reach the saccade target. So, it seems that
extra-retinal information is still available for saccade execution after a lesion to the parietal lobe. Here, we investigated whether extra-retinal signals are also available for
perceptual judgements in nine patients with strokes affecting the posterior parietal cortex.
We assessed perceptual continuity with the intra-saccadic displacement task. We exploited the increased sensitivity when a small temporal blank is introduced after saccade
offset (blank effect). The blank effect is thought to reflect the availability of extra-retinal
signals for perceptual judgements. Although patients exhibited a relative difference to
control subjects, they still demonstrated the blank effect. The data suggest that a lesion to the posterior parietal cortex (PPC) alters the processing of extra-retinal signals but does not
abolish their influence altogether