Electrophysiological recordings in monkeys have now revealed several brain regions that contain bimodal visuotactile neurons capable of responding to either tactile or visual stimuli placed on or near the hands, arms, and face. These cells have now been found in frontal, parietal, and subcortical areas of the monkey brain, suggesting a cortical network of neurons that preferentially represent near peripersonal space. The degree to which the visual responses of such cells rely on input from the primary visual cortex and the extent to which they may contribute to visual perception is not completely understood. Nonetheless, recent neuropsychological studies suggest that a similar representation of near space may be bimodally coded in humans as well. Given the accumulating evidence for specialized processing of visual stimuli placed near the hands and arms, we hypothesized that arm position may be capable of modulating human visual ability. Here we report the case of WM, who lost his ability to see in his left visual hemifield after sustaining damage to his right primary visual cortex. Interestingly, the placement of WM's left arm into his "blind" field resulted in significantly better detection of left visual field stimuli compared to when his hand was placed in his lap at midline. Moreover, we found this attenuation to be confined to stimuli presented within reaching distance (unless a tool that extended WM's reach was held while he performed the test). These findings are highly consistent with the characteristics of the bimodal visuo-tactile neurons that have been described in monkeys. Thus, it seems that arm position can modulate human visual ability, even after damage to the primary visual cortex. This study provides an exciting bridge between monkey neurophysiology and human visual capacity while also offering a novel approach for improving visual defects acquired via cortical injury.

Increased computer use in clinical settings offers an opportunity to develop new neuropsychological tests that exploit the control computers have over stimulus dimensions and timing. However, before adopting new tools, empirical validation is necessary. In the current study, our aims were twofold: to describe a computerized adaptive procedure with broad potential for neuropsychological investigations, and to demonstrate its implementation in testing for visual hemispatial neglect. Visual search results from adaptive psychophysical procedures are reported from 12 healthy individuals and 23 individuals with unilateral brain injury. Healthy individuals reveal spatially symmetric performance on adaptive search measures. In patients, psychophysical outcomes (as well as those from standard paper-and-pencil search tasks) reveal visual hemispatial neglect. Consistent with previous empirical studies of hemispatial neglect, lateralized impairments in adaptive conjunction search are greater than in adaptive feature search tasks. Furthermore, those with right hemisphere damage show greater lateralized deficits in conjunction search than do those with left hemisphere damage. We argue that adaptive tests, which automatically adjust to each individual's performance level, are efficient methods for both clinical evaluations and neuropsychological investigations and have the potential to detect subtle deficits even in chronic stages, when flagrant clinical signs have frequently resolved. (JINS, 2008, 14, 243-256.)

Brain damage often results in visual defects and/or higher order visuo-spatial disorders including the syndromes of unilateral neglect and extinction. These syndromes and their associated behavioral sequelae are described along with several standard assessments and methods for behaviorally quantifying such deficits. In particular, the advantages of the reaction time measures commonly used by cognitive neuroscientists are surveyed. In order to illustrate how reaction time measures can be used to examine the subtleties of visuo-spatial deficits, several reaction time studies that have been conducted in patients with neglect and/or extinction are discussed. These studies stand as an example of how reaction time measures can contribute to both clinical and experimental neuropsychology.

These neurobiologicalstudies have provided evidence that attention modulates perceptual processing at various levels in the visual system. Yet, how and when attention is directed remains a topic of investigation.Behavioral studies have contributed extensively toward an understanding of attention by exploring which aspects of the visual environment are selected. For instance, evidence has accumulated in support of object-based mechanisms of attention in addition to space-based mechanisms (Behrmann, Zemel, & Mozer, 1998;Duncan, 1984;Egly, Driver, & Rafal, 1994;Jordan & Tipper, 1998a, 1998bMarshall & Halligan, 1993;Moore, Yantis, & Vaughan, 1998;Tipper & Behrmann, 1996;Tipper & Weaver, 1998;Treisman, Kahneman, & Burkell, 1983). An understanding of the degree to which these two types of attention may be separate or complementary will ultimately aid our understanding of the neural circuitry and cognitive architecture of visual attention. However, achieving this understanding has been difficult (see Baylis & Driver, 1993;Buxbaum, Coslett, Montgomery, & Farah, 1996;Kim & Cave, 1995;Kramer, Weber, & Watson, 1997;Vecera, 1994Vecera, , 1997Vecera & Farah, 1994). The Where / What DistinctionNeurobiological evidence in support of a distinction between object and location processing in the visual system comes from studies of brain-damaged patients and anatomical studies in monkeys. Investigations of neurological patients have revealed compelling dissociations between object localization and object identification abilities (Farah, 1990;Robertson, Treisman, Friedman-Hill, & Grabowecky, 1997). The neural basis of these dissociations has been attributed to complementary pathways for visual analysis-namely, a dorsal where pathway that is important for analyzing the location and movement of visual stimuli and a ventral what pathway that is more involved in object identification (Mishkin, Ungerleider, & Macko, 1983;Ungerleider & Haxby, 1994).A similar distinction appears in the attention literature in the debate between attentional selection of objects and 577Copyright 2001 Psychonomic Society, Inc. Anatomical, physiological, and behavioral studies provide support for separate object-and locationbased components of visual attention. Although studies of object-based components have usually involved voluntary attention, more recent evidence has suggested that objects may play an independent role in reflexive exogenous orienting, at least at long stimulus onset asynchronies (SOAs). In the present experiments, the role of objects in reflexive attentional orienting was investigated by developing a task in which location and object cuing could be separately examined for both short and long SOAs. Typical location cuing effects were obtained, indicating facilitation at short cue-target intervals and inhibition of return (IOR) at longer intervals. In contrast, object cuing resulted in facilitation for cued objects at long cue-target intervals and no object-based IOR. Interestingly,object cuing primarily affected targets at cued locations, a...