We examined the effect of a task-irrelevant dimension on response times in young adults and senio... more We examined the effect of a task-irrelevant dimension on response times in young adults and seniors. We used the Simon task with congruent trials where the target and manual response were on the same side, incongruent trials where the target and response were on opposite sides, and neutral trials where the target appeared along the vertical meridian. We observed two age-related effects. First, there was a larger congruency effect in senior participants that was driven by greater interference; namely, their responses were slower on incongruent relative to neutral trials. Second, there was a Gratton effect; namely, a diminished Simon effect was found in young adults but not in seniors when the preceding trial was incongruent. However, these effects of aging were normalised when the inter-trial interval was increased; the Simon effect and interference were reduced and a Gratton effect appeared for seniors. We conclude that aging may impair the ability to quickly adapt to changing envir...
What limits the ability to attend several locations simultaneously? There are two possibilities: ... more What limits the ability to attend several locations simultaneously? There are two possibilities: Either attention cannot be divided without incurring a cost, or spatial memory is limited and observers forget which locations to monitor. We compared motion discrimination when attention was directed to one or multiple locations by briefly presented central cues. The cues were matched for the amount of spatial information they provided. Several random dot kinematograms (RDKs) followed the spatial cues; one of them contained task-relevant, coherent motion. When four RDKs were presented, discrimination accuracy was identical when one and two locations were indicated by equally informative cues. However, when six RDKs were presented, discrimination accuracy was higher following one rather than multiple location cues. We examined whether memory of the cued locations was diminished under these conditions. Recall of the cued locations was tested when participants attended the cued locations a...
When judging the 3D shape of a shaded image, observers generally assume that the light source is ... more When judging the 3D shape of a shaded image, observers generally assume that the light source is placed above and to the left. This leftward bias has been attributed to experiential factors shaped by the observers' handedness or hemispheric dominance. Others have found that experiential factors can rapidly modify the direction of the assumed light source, suggesting a role for learning in shaping perceptual expectations. In the current study, instead, we assessed the contribution of cultural factors affecting the way visual scenes are customarily inspected, in determining the assumed light source direction. Left- and right-handed first language English and Hebrew participants, who read and write from left to right and from right to left, respectively, judged the relative depth of the central hexagon surrounded by six shaded hexagons. We found a left bias in first language English participants, but a significantly smaller one in Hebrew participants. In neither group was the light...
A dual-task experiment was designed to determine whether attentional effects are modulated by the... more A dual-task experiment was designed to determine whether attentional effects are modulated by the size of the exogenous cue. A random-dot kinematogram (RDK), containing 100 white dots, was presented in each visual quadrant. In one RDK, the dots moved in a coherent direction for 200ms. On 50% of the trials, one of the dots in one RDK turned red. Participants reported the direction of coherent motion and the location or absence of the colour probe, and accuracy was measured. In the first experiment the exogenous cue was a luminance-change frame surrounding the RDK, ‘flashing’ for 80ms. The cue was uninformative for both the location of the coherent motion and the location of the colour probe. A validity effect was found for the motion discrimination, but not probe localisation. In the second experiment, the cue frame only surrounded the central region of the RDK, to spatially match the probe stimulus. The red dot probe was confined to the same central region of each RDK. A validity effect was evident for both tasks. A third experiment was conducted to ensure that the difference between Experiments 1 and 2 was due to the cue, rather than probe location uncertainty. The cue surrounded the RDK as in Experiment 1, but the probe was confined to the central portion of the RDKs as in Experiment 2. As in Experiment 1, there was only a validity effect for the motion discrimination task, confirming that exogenous spatial attention is affected by the size of the cue. These results suggest that the size of the exogenous cue must match the size of the stimulus in order to have an effect.
Unilateral spatial neglect (neglect) is a syndrome characterized by perceptual deficits that prev... more Unilateral spatial neglect (neglect) is a syndrome characterized by perceptual deficits that prevent patients from attending and responding to the side of space and of the body opposite a damaged hemisphere (contralesional side). Neglect also involves motor deficits: patients may be slower to initiate a motor response to targets appearing in the left hemispace, even when using their unaffected arm (directional hypokinesia). Although this impairment is well known, its anatomical correlate has not been established. We tested 52 patients with neglect after right hemisphere stroke, and conducted an anatomical analysis on 29 of them to find the anatomical correlate of directional hypokinesia. We found that patients with directional hypokinesia had a lesion involving the ventral lateral putamen, the claustrum, and the white matter underneath the frontal lobe. Most importantly, none of the patients without directional hypokinesia had a lesion in the same region. The localization of neglect's motor deficits to the basal ganglia establishes interesting homologies with animal data; it also suggests that a relative depletion of dopamine in the nigrostriatal pathway on the same side of the lesion may be an important pathophysiological mechanism potentially amenable to intervention.
The Quarterly Journal of Experimental Psychology, 2013
Inhibition of return (IOR)-a slow response to targets at recently attended locations, is believed... more Inhibition of return (IOR)-a slow response to targets at recently attended locations, is believed to play an important role in guiding behaviour. In the attention literature it has been shown that attentional capture by an exogenous cue affects contrast sensitivity so that it alters the appearance of low-contrast stimuli. Despite a significant amount of work over the last quarter century on IOR, it is not yet clear whether IOR operates in the same way. In the current study we examined the effect of IOR on contrast sensitivity-a very early, low-level perceptual process. We found in both a detection task and an orientation discrimination task that lower contrast was needed to detect the stimulus (Experiment 1) and determine its orientation (Experiment 2) at the cued location than at the uncued location, at short cue-target delays, while higher contrast was needed at long delays-reflecting IOR. These results clearly demonstrate that IOR affects contrast sensitivity in a similar way as attentional capture does and suggest that IOR increases perceived contrast of an object in the uncued location.
The Quarterly Journal of Experimental Psychology, 2013
Exogenous attention is an involuntary, reflexive orienting response that results in enhanced proc... more Exogenous attention is an involuntary, reflexive orienting response that results in enhanced processing at the attended location. The standard view is that this enhancement generalizes across visual properties of a stimulus. We test whether the size of an exogenous cue sets the attentional field and whether this leads to different effects on stimuli with different visual properties. In a dual task with a random-dot kinematogram (RDK) in each quadrant of the screen, participants discriminated the direction of moving dots in one RDK and localized one red dot. Precues were uninformative and consisted of either a large or a small luminance-change frame. The motion discrimination task showed attentional effects following both large and small exogenous cues. The red dot probe localization task showed attentional effects following a small cue, but not a large cue. Two additional experiments showed that the different effects on localization were not due to reduced spatial uncertainty or suppression of RDK dots in the surround. These results indicate that the effects of exogenous attention depend on the size of the cue and the properties of the task, suggesting the involvement of receptive fields with different sizes in different tasks. These attentional effects are likely to be driven by bottom-up mechanisms in early visual areas.
Proceedings of the National Academy of Sciences, 2005
Four subjects took part in the experiment. Each subject was scanned in seven to eight separate 3-... more Four subjects took part in the experiment. Each subject was scanned in seven to eight separate 3-h sessions and completed between 814 and 990 trials. Written consent was obtained before each behavioral and imaging session. The experimental protocol was approved by the Washington University Human Studies Review Board.
Inhibition of return (IOR) is a mechanism whereby the attentional system favors novel locations b... more Inhibition of return (IOR) is a mechanism whereby the attentional system favors novel locations by inhibiting already scanned ones. An important question is what the neural structures are involved. Recently, we studied a patient with damage to the superior colliculus (SC) and concluded that the SC generates IOR. However, it is possible that IOR is generated beyond the colliculus, for example, by the pulvinar. In this paper we tested three patients with unilateral damage to the pulvinar and demonstrated that the pulvinar is not necessary for IOR generation, providing additional support to the suggestion that the SC generates IOR. In addition, since we used monocular presentation, we were able to furnish behavioral evidence for nasal-temporal asymmetrical representation of visual input in the pulvinar.
This research examined 2 components of visual orienting in medicated schizophrenia patients: the ... more This research examined 2 components of visual orienting in medicated schizophrenia patients: the validity effect and the inhibition of return (IOR). In the 1st experiment, patients showed the expected asymmetry in orienting attention, that is, larger validity effect in the right visual field than in the left. However, this asymmetry was due to a deficit in facilitatory processes rather than a disengagement deficit. In addition, patients showed a deficit in IOR. In the 2nd experiment, a 2nd central cue for summoning attention, explicitly, back to the center was used. In this experiment, normal IOR in schizophrenia patients was found. Because it was shown that schizophrenia patients do not have a disengagement deficit, IOR possibly could not be observed because of the increased facilitation in that location. It was proposed that the abnormality in visual attention in schizophrenia is due to a deficit in inhibitory processes.
Patients with schizophrenia show attention deficit characterized by a larger validity effect (fas... more Patients with schizophrenia show attention deficit characterized by a larger validity effect (fast responses to cued than uncued stimuli) in the right visual field than in the left visual field. In addition, schizophrenia patients do not show inhibition of return (IOR-a mechanism that enables efficient visual search), unless attention is summoned back to the center after the peripheral cue. The present study examined the short-term effect of neuroleptic medications on these two components of visual spatial attention in schizophrenia patients. In order to do this we tested schizophrenia patients that were treated with long-acting neuroleptic medication. These patients were treated once a month, which allowed us to test them with either low or high levels of medication. Here we show that neuroleptic medications reverse the attentional hemispheric asymmetry. In the group with a high level of medication fast RTs to cued trials were found in the right visual field, while in the group with a low level of medication the opposite pattern was found -fast RTs to cued trials were found in the left visual field. In addition, level of medication did not influence IORregardless of the level of medication, IOR was observed only when attention was summoned back to the center, unlike control group. These finding suggest an imbalance in dopaminergic activity, possibly in subcortical structures such as the basal ganglia. This study also shows a dissociation between the two components of visual orienting of attention and suggests that facilitation and inhibition are independent processes.
The syndrome of spatial neglect is typically associated with focal injury to the temporoparietal ... more The syndrome of spatial neglect is typically associated with focal injury to the temporoparietal or ventral frontal cortex. This syndrome shows spontaneous partial recovery, but the neural basis of both spatial neglect and its recovery is largely unknown. We show that spatial attention deficits in neglect (rightward bias and reorienting) after right frontal damage correlate with abnormal activation of structurally intact dorsal and ventral parietal regions that mediate related attentional operations in the normal brain. Furthermore, recovery of these attention deficits correlates with the restoration and rebalancing of activity within these regions. These results support a model of recovery based on the re-weighting of activity within a distributed neuronal architecture, and they show that behavioral deficits depend not only on structural changes at the locus of injury, but also on physiological changes in distant but functionally related brain areas.
& Maintaining a coherent percept of the visual scene while eye position continuously changes requ... more & 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 coor-dinates. 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. &
Parietal cortex has been implicated in the updating, after eye movements, of a salience map that ... more Parietal cortex has been implicated in the updating, after eye movements, of a salience map that is required for coherent visual experience and for the control of visually guided behavior. The current experiment investigated whether TMS over anterior intraparietal cortex (AIPCx), just after a saccade, would affect the ability to update and maintain a salience map. In order to generate a salience map, we employed a paradigm in which an uninformative cue was presented at one object in a display to generate inhibition of return (IOR)-an inhibitory tag that renders the cued object less salient than others in the display, and that slows subsequent responses to visual transients at its location. Following the cue, participants made a saccade to either left or right, and we then probed for updating of the location of IOR by measuring manual reaction time to targets appearing at cued location of the cued compared to an uncued object. Between the time of saccade initiation and target appearance, dual-pulse TMS was targeted over right (Experiment 1) or left AIPCx (Experiment 2), and a vertex control side. Updating of the location of IOR was eliminated by TMS over right, but not the left, AIPCx, suggesting that right parietal cortex is involved in the remapping of IOR. Remapping was eliminated by right AIPCx, regardless of whether the saccade was made to the left (contralateral), or right (ipsilateral) visual field, and regardless of which field the target appeared in. We conclude that right AIPCx is the neural substrate for maintaining a salience map across saccades, and not simply for propagating an efference copy of saccade commands.
Purpose: To assess the importance of 'disengagement failure' and 'attentional gradient' in unilat... more Purpose: To assess the importance of 'disengagement failure' and 'attentional gradient' in unilateral spatial neglect (USN) and in recovery from neglect. Method: Eight right-hemisphere-damaged stroke patients performed the standardized Behavioural-Inattention-Test battery for visual neglect, line-bisection tests, and two computerized reaction-time (RT) tasks: a variant of Posner's 'Spatial-Cueing' paradigm (with special emphasis on the magnitude of leftward disengagement time) and a signal-detection task (marking the spatial gradient of attention by the distribution of RTs to target stimuli in different spatial locations). The correlation between the different measures was assessed at two points in time, before and after a period of rehabilitation treatment. Results: A recovery pattern could be identified in both RT paradigms. However, the correlation between standard measures of neglect and performance on both, spatial-cueing and signal-detection tasks, was weak. Conclusion: Neither difficulty disengaging attention from an ipsilesional stimulus nor changes in the attentional gradient can fully explain the processes underlying USN and its recovery. A large interpersonal variance exists among USN patients in the expression of disengagement and other spatialattention deficits. Hence, individual patients should be tested by measuring different factors known to play a role in USN. This information is crucial for assigning the appropriate treatment for each patient in accord with the specific deficit revealed.
We examined the effect of a task-irrelevant dimension on response times in young adults and senio... more We examined the effect of a task-irrelevant dimension on response times in young adults and seniors. We used the Simon task with congruent trials where the target and manual response were on the same side, incongruent trials where the target and response were on opposite sides, and neutral trials where the target appeared along the vertical meridian. We observed two age-related effects. First, there was a larger congruency effect in senior participants that was driven by greater interference; namely, their responses were slower on incongruent relative to neutral trials. Second, there was a Gratton effect; namely, a diminished Simon effect was found in young adults but not in seniors when the preceding trial was incongruent. However, these effects of aging were normalised when the inter-trial interval was increased; the Simon effect and interference were reduced and a Gratton effect appeared for seniors. We conclude that aging may impair the ability to quickly adapt to changing envir...
What limits the ability to attend several locations simultaneously? There are two possibilities: ... more What limits the ability to attend several locations simultaneously? There are two possibilities: Either attention cannot be divided without incurring a cost, or spatial memory is limited and observers forget which locations to monitor. We compared motion discrimination when attention was directed to one or multiple locations by briefly presented central cues. The cues were matched for the amount of spatial information they provided. Several random dot kinematograms (RDKs) followed the spatial cues; one of them contained task-relevant, coherent motion. When four RDKs were presented, discrimination accuracy was identical when one and two locations were indicated by equally informative cues. However, when six RDKs were presented, discrimination accuracy was higher following one rather than multiple location cues. We examined whether memory of the cued locations was diminished under these conditions. Recall of the cued locations was tested when participants attended the cued locations a...
When judging the 3D shape of a shaded image, observers generally assume that the light source is ... more When judging the 3D shape of a shaded image, observers generally assume that the light source is placed above and to the left. This leftward bias has been attributed to experiential factors shaped by the observers' handedness or hemispheric dominance. Others have found that experiential factors can rapidly modify the direction of the assumed light source, suggesting a role for learning in shaping perceptual expectations. In the current study, instead, we assessed the contribution of cultural factors affecting the way visual scenes are customarily inspected, in determining the assumed light source direction. Left- and right-handed first language English and Hebrew participants, who read and write from left to right and from right to left, respectively, judged the relative depth of the central hexagon surrounded by six shaded hexagons. We found a left bias in first language English participants, but a significantly smaller one in Hebrew participants. In neither group was the light...
A dual-task experiment was designed to determine whether attentional effects are modulated by the... more A dual-task experiment was designed to determine whether attentional effects are modulated by the size of the exogenous cue. A random-dot kinematogram (RDK), containing 100 white dots, was presented in each visual quadrant. In one RDK, the dots moved in a coherent direction for 200ms. On 50% of the trials, one of the dots in one RDK turned red. Participants reported the direction of coherent motion and the location or absence of the colour probe, and accuracy was measured. In the first experiment the exogenous cue was a luminance-change frame surrounding the RDK, ‘flashing’ for 80ms. The cue was uninformative for both the location of the coherent motion and the location of the colour probe. A validity effect was found for the motion discrimination, but not probe localisation. In the second experiment, the cue frame only surrounded the central region of the RDK, to spatially match the probe stimulus. The red dot probe was confined to the same central region of each RDK. A validity effect was evident for both tasks. A third experiment was conducted to ensure that the difference between Experiments 1 and 2 was due to the cue, rather than probe location uncertainty. The cue surrounded the RDK as in Experiment 1, but the probe was confined to the central portion of the RDKs as in Experiment 2. As in Experiment 1, there was only a validity effect for the motion discrimination task, confirming that exogenous spatial attention is affected by the size of the cue. These results suggest that the size of the exogenous cue must match the size of the stimulus in order to have an effect.
Unilateral spatial neglect (neglect) is a syndrome characterized by perceptual deficits that prev... more Unilateral spatial neglect (neglect) is a syndrome characterized by perceptual deficits that prevent patients from attending and responding to the side of space and of the body opposite a damaged hemisphere (contralesional side). Neglect also involves motor deficits: patients may be slower to initiate a motor response to targets appearing in the left hemispace, even when using their unaffected arm (directional hypokinesia). Although this impairment is well known, its anatomical correlate has not been established. We tested 52 patients with neglect after right hemisphere stroke, and conducted an anatomical analysis on 29 of them to find the anatomical correlate of directional hypokinesia. We found that patients with directional hypokinesia had a lesion involving the ventral lateral putamen, the claustrum, and the white matter underneath the frontal lobe. Most importantly, none of the patients without directional hypokinesia had a lesion in the same region. The localization of neglect's motor deficits to the basal ganglia establishes interesting homologies with animal data; it also suggests that a relative depletion of dopamine in the nigrostriatal pathway on the same side of the lesion may be an important pathophysiological mechanism potentially amenable to intervention.
The Quarterly Journal of Experimental Psychology, 2013
Inhibition of return (IOR)-a slow response to targets at recently attended locations, is believed... more Inhibition of return (IOR)-a slow response to targets at recently attended locations, is believed to play an important role in guiding behaviour. In the attention literature it has been shown that attentional capture by an exogenous cue affects contrast sensitivity so that it alters the appearance of low-contrast stimuli. Despite a significant amount of work over the last quarter century on IOR, it is not yet clear whether IOR operates in the same way. In the current study we examined the effect of IOR on contrast sensitivity-a very early, low-level perceptual process. We found in both a detection task and an orientation discrimination task that lower contrast was needed to detect the stimulus (Experiment 1) and determine its orientation (Experiment 2) at the cued location than at the uncued location, at short cue-target delays, while higher contrast was needed at long delays-reflecting IOR. These results clearly demonstrate that IOR affects contrast sensitivity in a similar way as attentional capture does and suggest that IOR increases perceived contrast of an object in the uncued location.
The Quarterly Journal of Experimental Psychology, 2013
Exogenous attention is an involuntary, reflexive orienting response that results in enhanced proc... more Exogenous attention is an involuntary, reflexive orienting response that results in enhanced processing at the attended location. The standard view is that this enhancement generalizes across visual properties of a stimulus. We test whether the size of an exogenous cue sets the attentional field and whether this leads to different effects on stimuli with different visual properties. In a dual task with a random-dot kinematogram (RDK) in each quadrant of the screen, participants discriminated the direction of moving dots in one RDK and localized one red dot. Precues were uninformative and consisted of either a large or a small luminance-change frame. The motion discrimination task showed attentional effects following both large and small exogenous cues. The red dot probe localization task showed attentional effects following a small cue, but not a large cue. Two additional experiments showed that the different effects on localization were not due to reduced spatial uncertainty or suppression of RDK dots in the surround. These results indicate that the effects of exogenous attention depend on the size of the cue and the properties of the task, suggesting the involvement of receptive fields with different sizes in different tasks. These attentional effects are likely to be driven by bottom-up mechanisms in early visual areas.
Proceedings of the National Academy of Sciences, 2005
Four subjects took part in the experiment. Each subject was scanned in seven to eight separate 3-... more Four subjects took part in the experiment. Each subject was scanned in seven to eight separate 3-h sessions and completed between 814 and 990 trials. Written consent was obtained before each behavioral and imaging session. The experimental protocol was approved by the Washington University Human Studies Review Board.
Inhibition of return (IOR) is a mechanism whereby the attentional system favors novel locations b... more Inhibition of return (IOR) is a mechanism whereby the attentional system favors novel locations by inhibiting already scanned ones. An important question is what the neural structures are involved. Recently, we studied a patient with damage to the superior colliculus (SC) and concluded that the SC generates IOR. However, it is possible that IOR is generated beyond the colliculus, for example, by the pulvinar. In this paper we tested three patients with unilateral damage to the pulvinar and demonstrated that the pulvinar is not necessary for IOR generation, providing additional support to the suggestion that the SC generates IOR. In addition, since we used monocular presentation, we were able to furnish behavioral evidence for nasal-temporal asymmetrical representation of visual input in the pulvinar.
This research examined 2 components of visual orienting in medicated schizophrenia patients: the ... more This research examined 2 components of visual orienting in medicated schizophrenia patients: the validity effect and the inhibition of return (IOR). In the 1st experiment, patients showed the expected asymmetry in orienting attention, that is, larger validity effect in the right visual field than in the left. However, this asymmetry was due to a deficit in facilitatory processes rather than a disengagement deficit. In addition, patients showed a deficit in IOR. In the 2nd experiment, a 2nd central cue for summoning attention, explicitly, back to the center was used. In this experiment, normal IOR in schizophrenia patients was found. Because it was shown that schizophrenia patients do not have a disengagement deficit, IOR possibly could not be observed because of the increased facilitation in that location. It was proposed that the abnormality in visual attention in schizophrenia is due to a deficit in inhibitory processes.
Patients with schizophrenia show attention deficit characterized by a larger validity effect (fas... more Patients with schizophrenia show attention deficit characterized by a larger validity effect (fast responses to cued than uncued stimuli) in the right visual field than in the left visual field. In addition, schizophrenia patients do not show inhibition of return (IOR-a mechanism that enables efficient visual search), unless attention is summoned back to the center after the peripheral cue. The present study examined the short-term effect of neuroleptic medications on these two components of visual spatial attention in schizophrenia patients. In order to do this we tested schizophrenia patients that were treated with long-acting neuroleptic medication. These patients were treated once a month, which allowed us to test them with either low or high levels of medication. Here we show that neuroleptic medications reverse the attentional hemispheric asymmetry. In the group with a high level of medication fast RTs to cued trials were found in the right visual field, while in the group with a low level of medication the opposite pattern was found -fast RTs to cued trials were found in the left visual field. In addition, level of medication did not influence IORregardless of the level of medication, IOR was observed only when attention was summoned back to the center, unlike control group. These finding suggest an imbalance in dopaminergic activity, possibly in subcortical structures such as the basal ganglia. This study also shows a dissociation between the two components of visual orienting of attention and suggests that facilitation and inhibition are independent processes.
The syndrome of spatial neglect is typically associated with focal injury to the temporoparietal ... more The syndrome of spatial neglect is typically associated with focal injury to the temporoparietal or ventral frontal cortex. This syndrome shows spontaneous partial recovery, but the neural basis of both spatial neglect and its recovery is largely unknown. We show that spatial attention deficits in neglect (rightward bias and reorienting) after right frontal damage correlate with abnormal activation of structurally intact dorsal and ventral parietal regions that mediate related attentional operations in the normal brain. Furthermore, recovery of these attention deficits correlates with the restoration and rebalancing of activity within these regions. These results support a model of recovery based on the re-weighting of activity within a distributed neuronal architecture, and they show that behavioral deficits depend not only on structural changes at the locus of injury, but also on physiological changes in distant but functionally related brain areas.
& Maintaining a coherent percept of the visual scene while eye position continuously changes requ... more & 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 coor-dinates. 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. &
Parietal cortex has been implicated in the updating, after eye movements, of a salience map that ... more Parietal cortex has been implicated in the updating, after eye movements, of a salience map that is required for coherent visual experience and for the control of visually guided behavior. The current experiment investigated whether TMS over anterior intraparietal cortex (AIPCx), just after a saccade, would affect the ability to update and maintain a salience map. In order to generate a salience map, we employed a paradigm in which an uninformative cue was presented at one object in a display to generate inhibition of return (IOR)-an inhibitory tag that renders the cued object less salient than others in the display, and that slows subsequent responses to visual transients at its location. Following the cue, participants made a saccade to either left or right, and we then probed for updating of the location of IOR by measuring manual reaction time to targets appearing at cued location of the cued compared to an uncued object. Between the time of saccade initiation and target appearance, dual-pulse TMS was targeted over right (Experiment 1) or left AIPCx (Experiment 2), and a vertex control side. Updating of the location of IOR was eliminated by TMS over right, but not the left, AIPCx, suggesting that right parietal cortex is involved in the remapping of IOR. Remapping was eliminated by right AIPCx, regardless of whether the saccade was made to the left (contralateral), or right (ipsilateral) visual field, and regardless of which field the target appeared in. We conclude that right AIPCx is the neural substrate for maintaining a salience map across saccades, and not simply for propagating an efference copy of saccade commands.
Purpose: To assess the importance of 'disengagement failure' and 'attentional gradient' in unilat... more Purpose: To assess the importance of 'disengagement failure' and 'attentional gradient' in unilateral spatial neglect (USN) and in recovery from neglect. Method: Eight right-hemisphere-damaged stroke patients performed the standardized Behavioural-Inattention-Test battery for visual neglect, line-bisection tests, and two computerized reaction-time (RT) tasks: a variant of Posner's 'Spatial-Cueing' paradigm (with special emphasis on the magnitude of leftward disengagement time) and a signal-detection task (marking the spatial gradient of attention by the distribution of RTs to target stimuli in different spatial locations). The correlation between the different measures was assessed at two points in time, before and after a period of rehabilitation treatment. Results: A recovery pattern could be identified in both RT paradigms. However, the correlation between standard measures of neglect and performance on both, spatial-cueing and signal-detection tasks, was weak. Conclusion: Neither difficulty disengaging attention from an ipsilesional stimulus nor changes in the attentional gradient can fully explain the processes underlying USN and its recovery. A large interpersonal variance exists among USN patients in the expression of disengagement and other spatialattention deficits. Hence, individual patients should be tested by measuring different factors known to play a role in USN. This information is crucial for assigning the appropriate treatment for each patient in accord with the specific deficit revealed.
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Papers by Ayelet Sapir