Maintaining a coherent percept of the visual scene while eye position continuously changes requires that saccades be accompanied by remapping of the visual environment. We studied saccadic remapping in patients with unilateral lesions in the intraparietal sulcus and healthy controls, using inhibition of return (IOR)—an inhibitory tag that enables efficient visual search. In healthy controls, IOR was found at both retinal and environmental locations of the cue, indicating that the inhibitory tag had been remapped into environmental coordinates. In contrast, right parietal patients demonstrated IOR only at the retinal location of the cue, indicating that the intraparietal sulcus is involved in remapping of the environment after eye movements to afford a stable, environmentally based reference frame. Note that patients did not show environmental IOR in either visual field. These results also suggest that this region may be the neural substrate for encoding inhibitory spatial tags in an environmentally based reference frame.

We examined the effects of chronic unilateral lesions to either the inferior parietal lobe, or to the dorsolateral prefrontal cortex including the frontal eye fields (FEFs), upon human visual perception and saccades in temporal-order-judgment (TOJ) tasks. Two visual events were presented on each trial, one in each hemifield at various stimulus onset asynchronies (SOAs). In the saccade task, patients moved their eyes to whichever stimulus attracted gaze first. In the perceptual-manual task, they pressed a button to indicate which stimulus was perceived first. Frontal patients showed appropriate TOJs for visual targets in both tasks. Parietal patients showed appropriate TOJs in the perceptual-manual but not the saccade task; their saccades tended to be ipsilesional unless the contralesional target led substantially. This reveals a bias in saccade choice after parietal damage that cannot be attributed to deficient visual perception. These results challenge previous claims that only anterior lesions produce motoric spatial biases in humans. However, they are in accord with recent neurophysiological evidence for parietal involvement in saccade generation, and also with suggestions that visuomotor transformations in the parietal lobe serving direct spatial motor responses can dissociate from conscious perception as indicated by indirect arbitrary responses.

We present a longitudinal neuropsychological study (31 examinations over a period of 18 months) of patient DF. DF demonstrated bilateral atrophy of the hippocampal formation and globus pallidus resulting from carbon monoxide poisoning. Eighteen months after the event, the volume of the hippocampal formation was reduced by 42% on the left side and 28% on the right. The patient initially presented with a severe global amnesia. Then, he showed a gradual, yet selective recovery of episodic memory function. Verbal free recall and spatial memory performance remained reduced, whereas immediate word recall and recognition memory, as well as picture learning and memory, improved to levels at the lower range of normal performance. Interestingly, nonspatial associative learning was never much impaired and recovered completely by the end of testing. These data are taken as evidence that the human hippocampal formation does not equally support different forms of episodic memory.

To determine whether the parietal lobes contribute to the selection of nonspatial features known to be processed in the ventral stream, the current study examined the effect of chronic unilateral parietal lobe lesions in humans on color and location priming. Patients and normal controls performed a go/no-go color discrimination task in which either the same color and different color pairs of stimuli (prime and probe) were projected sequentially either in the same hemifield or in opposite hemifields. Control subjects and patients both showed independent effects of color and location priming. In the patients, primes in either field produced color priming for target probes in the ipsilesional field but not for probes in the contralesional field. This observation implicates the parietal cortex in processing activated codes of stimulus attributes not only for spatial information but also for visual features processed in the ventral visual pathways.

Nine patients with chronic, unilateral lesions of the dorso-lateral prefrontal cortex including the frontal eye fields (FEF) made saccades toward contralesional and ipsilesional fields. The saccades were either voluntarily directed in response to arrows in the center of a visual display, or were reflexively summoned by a peripheral visual signal. Saccade latencies were compared to those made by seven neurologic control patients with chronic, unilateral lesions of dorsolateral prefrontal cortex sparing the FEF, and by 13 normal control subjects. In both the normal and neurologic control subjects, reflexive saccades had shorter Latencies than voluntary saccades. In the FEF lesion patients, voluntary saccades had longer latencies toward the contralesional field than toward the ipsilesional field. The opposite pattern was found for reflexive saccades: latencies of saccades to targets in the contralesional field were shorter than saccades summoned to ipsilesional targets. Reflexive saccades toward the ipsilesional field had abnormally prolonged latencies; they were comparable to the latencies observed for voluntary Saccades. The effect of FEF lesions on saccacles contrasted with those observed in a second experiment requiring a key press response: FEF lesion patients were slower in making key press responses to signals detected in the contralesional field. To assess covert attention and preparatory set the effects of precues providing advance information were measured in both saccade and key press experiments. Neither patient group showed any deficiency in using precues to shift attention or to prepare saccades. The FEF facilitates the generation of voluntary saccatles and also inhibits reflexive saccades to exogenous signals. FEF lesions may disinhibit the ipsilesional midbrain which in turn may inhibit the opposite colliculus to slow reflexive saccades toward the ipsilesional field.

Evidence is presented that the phylogenetically older retin-otectal pathway contributes to reflex orienting of visual attention in normal human subjects. The study exploited a lateralized neuroanatomic arrangement of retinotectal pathways that distinguishes them from those of the geniculostriate system; namely, more direct projections to the colliculus from the temporal hemifield. Subjects were tested under monocular viewing conditions and responded to the detection of a peripheral signal by making either a saccade to it or a choice reaction time manual keypress. Attention was summoned by noninformative peripheral precues, and the benefits and costs of attention were calculated relative to a central precue condition. Both the benefits and costs of orienting attention were greater when attention was summoned by signals in the temporal hemifield. This temporal hemifield advantage was present for both saccade and manual responses. These findings converge with observations in patients with occipital and midbrain lesions to show that the phylogenetically older retinotectal pathway retains an important role in controlling visually guided behavior; and they demonstrate the usefulness of temporal-nasal hemifield asymmetries as a marker for investigating extrageniculate vision in humans.