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The pre-motor theory suggests that, when attention is oriented to a location, the motor systems that are involved in achieving current behavioural goals are activated. For example, when a task requires accurate reaching, attention to a location activates the motor circuits controlling saccades and manual reaches. These actions involve separate neural systems for the control of eye and hand, but we believe that the selection processes acting on neural population codes within these systems are similar and can affect each other. The attentional effect can be revealed in the subsequent movement. The present study shows that the path the eye takes as it saccades to a target is affected by whether a reach to the target is also produced. This effect is interpreted as the influence of a hand-centred frame used in reaching on the spatial frame of reference required for the saccade.

Research with normal participants has demonstrated that mechanisms of selective attention can simultaneously gain access to internal representations of spatial information defined with respect to both location- and object-based frames of reference. The present study demonstrates that patients with unilateral spatial neglect following a right-hemisphere lesion are poorer at detecting information on the contralateral left side in both location- and object-based spatial coordinates simultaneously. Moreover, the extent of the neglect is modulated by the probability of a target's appearing in either reference frame; as the probability of sampling a target in a particular frame of reference increases, so does the severity of neglect in the frame. These findings suggest that attention can be flexibly and strategically assigned to a reference frame depending on the contingencies of the task.

We investigated whether inhibition of return (IOR) could be observed in location-based, scene-based, and object-centered frames of reference. IOR was found to move both with a separate cued object (scene-based) and with a location within a single rotating object (object-centered). Importantly, however, IOR was also associated with the environmental location cued when cuing was of a separate object (scene-based), whereas facilitation of the cued location was found when cuing was of a component within an object. These results suggest that location is of central importance to scene-based representations of separate objects, which appear to be encoded in viewer-centered coordinates, whereas environmental locus is of little relevance when attention orients within a single object. The results also provide further evidence for the coexistence of both excitation and inhibition associated with uninformative exogenous cues.

The perception of tactile stimuli is facilitated when subjects look towards the stimulated body site: this facilitation even takes place when visual information is unavailable, as when orienting in the dark. It is not known whether the facilitation is due entirely to such proprioceptive orienting of eye and head, or whether visual information of the body site can also facilitate touch. An experiment is reported which dissociates vision and proprioception, and demonstrates for the first time that vision of a body part, independent of proprioceptive orienting, can indeed effect somatosensation.

Subjects reached for visual target lights in the presence of distractor lights. Previous studies (e.g., Tipper, Lortie, & Baylis, 1992) have shown that distractors at locations between the starting position of the hand and the target location caused greater interference (as indexed by response time) than distractors beyond the target. This finding has been attributed to the former distractors being in the path of the response to the target, but we provide evidence that they interfere more because of their proximity to the starting position of the hand (a "proximity-to-hand effect"). Also, distractors located in the hemispace ipsilateral to the responding hand caused more interference than contralateral distractors (an "ipsilateral effect"). The proximity-to-hand and ipsilateral effects were found in both reaction and movement time, suggesting that the resolution of the selection problem caused by a distractor could occur before or after movement initiation. Further evidence for this suggestion was provided by individual differences in movement initiation strategies which were predictive of the temporal locus of distractor influence. Errors of touching the distractor location also showed proximity-to-hand and ipsilateral effects. We discuss applications of these findings to real-world situations in which people reach for the wrong object in multiple-object visual displays.

Object-based attention was examined in 2 split-brain patients. A precued object could move within a visual field or cross the midline to the opposite field. Normal individuals show an inhibition in detecting signals in the cued object whether it moves within or between fields. Both patients showed this effect when the cued object moved within a visual field. When it crossed the midline into the opposite visual field, however, detection was faster in the cued box. These results reveal both facilitatory and inhibitory effects on attention that are object based and may last for several hundred milliseconds. However, the inhibition requires an intact corpus callosum for interhemispheric transfer, whereas the facilitation is transferred subcortically.

Whether visuospatial attention accesses object-centered representations, in addition to location-based coordinates, was investigated in patients with hemispatial neglect who detected a target on the left or right of a single object (2 connected circles or barbell) or of 2 objects (2 unconnected circles). The object or objects either remained static (left circle in left space) or rotated by 180 degrees (left circle now in right space). Relative to the static condition, in the rotating condition, detection times are facilitated on the left (contralateral) and inhibited on the right (ipsilateral) of space even when eye movements are controlled. This modulation of neglect was only observed for the single object, but not for the 2-object displays. The findings suggest that attention operates on object-centered as well as on location-based representations, and thus accesses multiple reference frames.

Representational momentum (RM) is a distortion in memory for the final position of an object in the direction implied by a set of discrete inducing displays (J.J. Freyd, 1987; J.J. Freyd & R.A. Finke, 1984). The effect has been shown under a wide variety of circumstances, which has led to assertions that it is a general enough phenomenon to extend to virtually any dimension of change. It is reported here that decisions about luminance seem not to be subject to RM. Instead, a robust effect in the direction opposite to that predicted by the RM hypothesis was observed. It is argued that RM might be more usefully considered limited to dimensions of change correlated with motion in the real world, and some initial hypotheses as to the nature of the mechanism underlying this new luminance effect are presented.

Most studies of selective attention briefly present static 2-dimensional stimuli and require arbitrary responses such as verbal naming or a keypress. Many of our perceptual-motor interactions with the environment, however, require reaching directly toward an object while ignoring other objects in the scene. A series of experiments examines selective attention in the latter reaching situation. Effects previously observed in the traditional experimental procedures were obtained, suggesting that the models developed (which propose inhibitory mechanisms, e.g.) apply to ecologically valid situations. Attention accesses action-centered internal representations during such tasks.

Our response to visual events can be delayed at positions we have recently examined attentively. Such inhibition could organize visual search through static scenes by suppressing those loci already searched, but this mechanism would fail in moving scenes as objects' locations then change during search. We cued attention to a moving object and found subsequent inhibition at the locus the object later occupied. This implies that previously examined objects are suppressed. Such object-centred inhibition would be highly adaptive, but would require a sophisticated neural implementation for a mechanism held to be sub-cortical.

Research studying visual selective attention has largely examined filtering tasks in which stationary targets are selected from stationary distractors by a physical cue such as location and identity is the reported attribute. During many interactions with the visual environment however, target stimuli are selected by what they are, whereas action is controlled by where the stimulus is located. This study demonstrates that the interference and negative priming effects observed in standard filtering tasks, which suggest that distractors are analyzed and subsequently inhibited during selection, are also observed when targets are selected on the basis of identity and spatial location is the reported attribute. Furthermore, experimental results suggest that inhibition associated with distracting objects in this new task is object-centered, so that if the object is moving through space, inhibition moves with it.