Electrophysiological correlates of visual binding errors after bilateral parietal damage

Disengagement of attention with spatial neglect: A systematic review of behavioral and anatomical findings

The present review examined the consequences of focal brain injury on spatial attention studied with cueing paradigms, with a particular focus on the disengagement deficit, which refers to the abnormal slowing of reactions following an ipsilesional cue. Our review supports the established notion that the disengagement deficit is a functional marker of spatial neglect and is particularly pronounced when elicited by peripheral cues. Recent research has revealed that this deficit critically depends on cues that have task-relevant characteristics or are associated with negative reinforcement. Attentional capture by task-relevant cues is contingent on damage to the right temporo-parietal junction (TPJ) and is modulated by functional connections between the TPJ and the right insular cortex. Furthermore, damage to the dorsal premotor or prefrontal cortex (dPMC/dPFC) reduces the effect of task-relevant cues. These findings support an interactive model of the disengagement deficit, involving the right TPJ, the insula, and the dPMC/dPFC. These interconnected regions play a crucial role in regulating and adapting spatial attention to changing intrinsic values of stimuli in the environment.

When Left is One and Right is Double: An Experimental Investigation of Visual Allesthesia after Right Parietal Damage

Illusory visual phenomena, such as palinopsia, polyopsia or allesthesia, are rare manifestations of posterior cortical damage. Symptoms are characterized by illusory perceptions, ranging from isolated stationary objects to scenes and moving persons. Such illusions may appear while the original object is still in view, or become manifest with a delay and last for minutes, hours or even days. Some authors have suggested a disinhibited cortical response underlying visual illusions, but experimental studies supporting this hypothesis are lacking. Here, we examined a rare patient who after focal right parietal injury consistently reported a second stimulus on the left when briefly shown a target in his right hemifield. The patient perceived the illusory stimulus as less intense, and therefore concluded that it must have a different shape than the original stimulus. A masking experiment revealed that the frequency of the illusion was inversely related to the visibility of the original stimulus, suggesting that it depended on early, feedforward visual processing. We propose that illusory perceptions reflect the interplay of two physiological processes: a fast and automatic activation of contralateral, homotopic visual cortex after unilateral stimulation, and the lack of top-down inhibition following damage to the posterior parietal cortex.