Transient binding by time: Neuropsychological evidence from anti-extinction

Anti-extinction occurs when there is poor report of a single stimulus presented on the contralesional side of space, but better report of the same item when it occurs concurrently with a stimulus on the ipsilesional side (Goodrich & Ward, 1997). We report a series of experiments that examine the factors that lead to anti-extinction in a patient GK, who has bilateral parietal lesions but more impaired identification of left-side stimuli. We show a pattern of anti-extinction when stimuli are briefly presented, which is followed by an extinction effect when stimuli are left for longer in the visual field. In Experiments 1 and 2 we present evidence that the anti-extinction effects are determined by stimuli onsetting together, and it is not apparent when stimuli are defined by offsets. In Experiments 3 and 4 we report that performance is not strongly affected by whether the same or different tasks are performed on the ipsi- and contralesional stimuli, and the anti-extinction effect also survives trials where eye movements are made to right-side stimuli. Experiment 5 provides evidence that anti-extinction is due to temporal grouping between stimuli, rather than to increased arousal or cueing attention to the contralesional side. Experiment 6 demonstrates that anti-extinction dissociates from GK's conscious perception of when contra- and ipsilesional stimuli occur together. We interpret the data as indicating that there is unconscious and transient temporal binding in vision.     

Visual extinction of similar and dissimilar stimuli: Evidence for level-dependent attentional competition

Repetition blindness (RB) is the failure to report a visual stimulus presented shortly after a first occurrence of the same stimulus (Kanwisher, 1987). A similar phenomenon is that visual extinction, the failure to identify a contralesional stimulus presented simultaneously with an ipsilesional stimulus, increases with increasing similarity between the contralesional and ipsilesional stimulus (Baylis, Driver, & Rafal, 1993). We report a patient who, after a right parietal stroke, presented increased extinction for letters in repeated (e.g., A + A) than in unrepeated (e.g., T + U) displays. Increased extinction due to RB was observed in all experimental conditions probing item identification and varied between 5.4% and 40.6% across conditions. RB was unaffected by temporal modulation of the display, but was significantly reduced when stimuli grouped by a surrounding contour. Identification of contralesional repeated and unrepeated letters could be enhanced by auditory cues presented prior to the visual display. These results suggest that perceptual processing of extinguished stimuli that are similar to the stimulus presented on the preserved side is relatively unimpaired, but that the patient fails to ascribe to the stimulus a separate identity, supporting the distinction between type recognition and token individuation (Kanwisher, 1987). The extinction patterns for similar and dissimilar stimuli indicate that competition for attentional selection does not only occur at low (perceptual) levels, but also at higher processing levels, suggesting the presence of attentional competition on different levels of analysis.     

Visual extinction of similar and dissimilar stimuli: Evidence for level-dependent attentional competition

Repetition blindness (RB) is the failure to report a visual stimulus presented shortly after a first occurrence of the same stimulus (Kanwisher, 1987). A similar phenomenon is that visual extinction, the failure to identify a contralesional stimulus presented simultaneously with an ipsilesional stimulus, increases with increasing similarity between the contralesional and ipsilesional stimulus (Baylis, Driver, & Rafal, 1993). We report a patient who, after a right parietal stroke, presented increased extinction for letters in repeated (e.g., A?+?A) than in unrepeated (e.g., T?+?U) displays. Increased extinction due to RB was observed in all experimental conditions probing item identification and varied between 5.4% and 40.6% across conditions. RB was unaffected by temporal modulation of the display, but was significantly reduced when stimuli grouped by a surrounding contour. Identification of contralesional repeated and unrepeated letters could be enhanced by auditory cues presented prior to the visual display. These results suggest that perceptual processing of extinguished stimuli that are similar to the stimulus presented on the preserved side is relatively unimpaired, but that the patient fails to ascribe to the stimulus a separate identity, supporting the distinction between type recognition and token individuation (Kanwisher, 1987). The extinction patterns for similar and dissimilar stimuli indicate that competition for attentional selection does not only occur at low (perceptual) levels, but also at higher processing levels, suggesting the presence of attentional competition on different levels of analysis.     

A deficit in contralesional object representation associated with attentional limitations after parietal damage

Stankiewicz, Hummel, and Cooper (1998) proposed that detailed coding of part-whole relations for objects is contingent on objects being attended. We report a neuropsychological test of this assertion. We examined the effects of left-right reflection on object matching in a group of patients with parietal damage and impaired attention to the contralesional side of space (Experiment 1). The patients were poor at matching objects subject to left-right reflection, relative to identical stimuli (Experiment 2). This was not due to a lack of sensitivity to information on the contralesional side. In a subsequent study, the patients were better at matching identical whole objects at fixation than when they just received half the object in their ipsilesional field (Experiment 3). However, unlike both nonlesioned controls and control patients with frontal lesions, the parietal patients were unaffected by altering the relative spatial locations of object features in their contralesional field (Experiment 4). The basic result, of poor performance with left-right-reflected items, was also replicated using a priming rather than an explicit matching procedure (Experiment 5). These results provide confirmation that visual attention, mediated by the posterior parietal cortex, is important for generating part-whole codes that facilitate the matching of mirror-reflected objects.     

Sensory and response contributions to visual awareness in extinction

Brain-damaged patients may extinguish contralesional stimuli when ipsilesional stimuli are presented simultaneously. Most theories of extinction postulate that stimuli compete for pathologically limited attentional resources with a bias to process ipsilesional over contralesional stimuli. Implicit in this view is the idea that responses follow the outcome of an earlier competition between inputs. In the current study of two patients, we used signal detection analyses to test the hypothesis that response criteria and response modalities also contribute to visual awareness. We found that identification was more sensitive than detection in uncovering deficits of contralesional awareness. Extinction was worse with bilateral stimuli when the ipsilesional stimulus was identical or similar to the target than when it was dissimilar. This diminished awareness was more likely to reflect a shift towards more conservative responses rather than diminished discrimination of contralesional stimuli. By contrast, one patient was better able to discriminate contralesional stimuli when using his contralesional limb to indicate awareness of targets than when using his ipsilesional limb. These data indicate that the nature of stimuli can modulate response criteria and the motor response can affect the sensory discriminability. Sensory discrimination and response output are not organized in a simple serial manner. Rather, input and output parameters interact in complicated ways to produce visual awareness. Visual awareness itself appears to be the outcome of two bottlenecks in processing, one having to do with sensory processing that may be covert and the other having to do with decision making, which by definition is overt. Finally, we advocate the use of signal detection analyses in studies of extinction, a method that has been surprisingly neglected in this line of research.     

A deficit in contralesional object representation associated with attentional limitations after parietal damage

Stankiewicz, Hummel, and Cooper (1998) proposed that detailed coding of part–whole relations for objects is contingent on objects being attended. We report a neuropsychological test of this assertion. We examined the effects of left–right reflection on object matching in a group of patients with parietal damage and impaired attention to the contralesional side of space (Experiment 1). The patients were poor at matching objects subject to left–right reflection, relative to identical stimuli (Experiment 2). This was not due to a lack of sensitivity to information on the contralesional side. In a subsequent study, the patients were better at matching identical whole objects at fixation than when they just received half the object in their ipsilesional field (Experiment 3). However, unlike both nonlesioned controls and control patients with frontal lesions, the parietal patients were unaffected by altering the relative spatial locations of object features in their contralesional field (Experiment 4). The basic result, of poor performance with left–right-reflected items, was also replicated using a priming rather than an explicit matching procedure (Experiment 5). These results provide confirmation that visual attention, mediated by the posterior parietal cortex, is important for generating part–whole codes that facilitate the matching of mirror-reflected objects.     

Interactions between perception and action programming: Evidence from visual extinction and optic ataxia

We report a series of 7 experiments examining the interaction between visual perception and action programming, contrasting 2 neuropsychological cases: a case of visual extinction and a case with extinction and optic ataxia. The patients had to make pointing responses to left and right locations, whilst identifying briefly presented shapes. Different patterns of performance emerged with the two cases. The patient with “pure” extinction (i.e., extinction without optic ataxia) showed dramatic effects of action programming on perceptual report. Programming an action to the ipsilesional side increased extinction (on 2-item trials) and tended to induce neglect (on 1-item trials); this was ameliorated when the action was programmed to the contralesional side. Separable effects of using the contralesional hand and pointing to the contralesional side were apparent. In contrast, the optic ataxic patient showed few effects of congruency between the visual stimulus and the action, but extinction when an action was programmed. This effect was particularly marked when actions had to be made to peripheral locations, suggesting that it reflected reduced resources to stimuli. These effects all occurred using stimulus exposures that were completed well before actions were effected. The data demonstrate interactions between action programming and visual perception. Programming an action to the affected side with the contralesional limb reduces “pure” extinction because attention is coupled to the end point of the action. However, in a patient with deficient visuo-motor coupling (optic ataxia), programming an action can increase a spatial deficit by recruiting resources away from perceptual processing. The implications for models of perception and action are discussed.     

Assessing the audiotactile Colavita effect in near and rear space

The Colavita effect occurs when participants performing a speeded detection/discrimination task preferentially report the visual component of pairs of audiovisual or visuotactile stimuli. To date, however, researchers have failed to demonstrate an analogous effect for audiotactile stimuli (Hecht and Reiner in Exp Brain Res 193:307–314, 2009). Here, we investigate whether an audiotactile Colavita effect can be demonstrated by manipulating either the physical features of the auditory stimuli presented in frontal (Experiment 1) or rear space (Experiment 3), or the relative and absolute position of auditory and tactile stimuli in frontal (Experiment 2) or rear space (Experiment 3). The participants showed no evidence of responding preferentially to one of the sensory components of the bimodal stimuli when they were presented from a single location in frontal space (Experiment 1). However, a significant audiotactile Colavita effect was demonstrated in Experiments 2 and 3, with participants preferentially reporting the auditory (rather than tactile) stimulus on the bimodal target trials. In Experiment 3, an audiotactile Colavita effect was reported for auditory white noise bursts but not for pure tones and selectively for those stimuli presented from the same (rather than from the opposite) side. Taken together, these results therefore suggest that when a tactile and an auditory stimulus are presented from a single frontal location, participants do not preferentially report one of the two sensory components (Experiment 1). In contrast, when the stimuli are presented from different locations, people preferentially report the auditory component, especially when they are spatially coincident (Experiments 2 and 3). Moreover, for stimuli presented from rear space, the Colavita effect was only observed for auditory stimuli consisting of white noise bursts (but not for pure tones), suggesting that this kind of stimuli are more likely to be bound together with somatosensory stimuli in rear space.     

Interactions between perception and action programming: evidence from visual extinction and optic ataxia

We report a series of 7 experiments examining the interaction between visual perception and action programming, contrasting 2 neuropsychological cases: a case of visual extinction and a case with extinction and optic ataxia. The patients had to make pointing responses to left and right locations, whilst identifying briefly presented shapes. Different patterns of performance emerged with the two cases. The patient with "pure" extinction (i.e., extinction without optic ataxia) showed dramatic effects of action programming on perceptual report. Programming an action to the ipsilesional side increased extinction (on 2-item trials) and tended to induce neglect (on 1-item trials); this was ameliorated when the action was programmed to the contralesional side. Separable effects of using the contralesional hand and pointing to the contralesional side were apparent. In contrast, the optic ataxic patient showed few effects of congruency between the visual stimulus and the action, but extinction when an action was programmed. This effect was particularly marked when actions had to be made to peripheral locations, suggesting that it reflected reduced resources to stimuli. These effects all occurred using stimulus exposures that were completed well before actions were effected. The data demonstrate interactions between action programming and visual perception. Programming an action to the affected side with the contralesional limb reduces "pure" extinction because attention is coupled to the end point of the action. However, in a patient with deficient visuo-motor coupling (optic ataxia), programming an action can increase a spatial deficit by recruiting resources away from perceptual processing. The implications for models of perception and action are discussed.     

The effect of gaze direction on sound localization in brain-injured and normal adults

This study examined the effects of eye position on sound localization in normal and brain lesion subjects. On the assumption that cerebral lesions may disrupt the representation of or attention to auditory space in the contralesional hemispace, we predicted that subjects with brain lesions would be less accurate in localizing sounds in the contralesional hemispace. In Experiment 1 we showed that gazing to the midline subjects with brain lesions were indeed impaired in localizing sounds in the contralesional hemispace. On the assumption that spatial attention is deployed at the site to which gaze is directed, we predicted that sound localization would be better on the side to which subjects directed their gaze. In Experiment 2, brain lesion subjects performed significantly better in the contralesional hemispace when they directed gaze to that hemispace. This improvement was accompanied by deterioration of performance in the ipsilesional hemispace. When subjects directed gaze to the ipsilesional hemispace, performance in the contralesional hemispace was further impaired. The effect of gaze was also observed in normal subjects in Experiments 2 and 3, independently of response mode (verbal versus pointing responses). These findings are consistent with the hypothesis that sound location may be mapped in eye-centered coordinates and that directing gaze to one hemispace reduces attentional allocation to the other hemispace.     

Anti-extinction Following Unilateral Parietal Damage

Following unilateral damage to the parietal cortex, extinction of sensory events on the side of space opposite the lesion frequently occurs: A contralesional event is detected when it occurs alone, but missed when it is accompanied by an ipsilesional event. We describe a patientwith left visuospatial neglect subsequent to a right parietal infarct, who shows the opposite of this typical extinction pattern: On brief visual presentations, he consistently shows better detection and identification of contralesional targets when they appear simultaneously with an ipsilesional target, compared to when the contralesional target appears alone. This benefitfor contralesional targets on simultaneous presentation is found most clearly when the same task is performed with both contra- and ipsilesional items. These findings first provide a very clear demonstration of neglect in the absence of extinction. Second, our results demonstrate that visuospatial neglect can be mitigated by non-perceptual task variables.     

When they see,they see it almost right: Normal subjective experience of detected stimuli in spatial neglect

Unilateral spatial neglect (USN) patients show reduced contrast sensitivity on their contralesional side and often miss their non-salient stimuli. What their subjective experience is when successfully reporting a stimulus remains unclear. Here, we report that despite large contrast sensitivity differences between the sides, the relative attenuation in perceived contrast measured in a contrast-matching task was small. This was true even at threshold levels where the patients missed up to 40% of the contralesional target patches, in contrast to a 100% detection rate on their ipsilesional side. When the misses were counted as zero perceived contrast events, the attenuation in perceived contrast was less than half of the sensitivity loss. When the misses were ignored, there was almost no attenuation in perceived contrast, implying that whenever the patients detected a target, they perceived it with the correct contrast. These findings suggest that contrast sensitivity reduction in USN is not due to attenuation occurring at a peripheral low-level processing stage. More likely it reflects a high-threshold added at a higher level of processing, which prevents sensory events from reaching conscious awareness. Hence, patients may often miss contralesional stimuli but see them in full contrast once they clear the high-level hurdle.     

Underestimation of contralateral space in neglect: a deficit in the “where” task

Space perception was investigated in right brain damaged patients with ( N=13) and without neglect ( N=5; control group). Patients were requested to localise a target tachistoscopically flashed at various eccentricities along the horizontal meridian. All patients had an intact visual field and spared ability to manually point to a target. To segregate magno- and parvo-pathway activity, stimuli modulated in either luminance or chromatic contrast were used. Patients were required to verbally report the stimulus position (verbal task) or to manually point to the stimulus (pointing task). Neglect patients reported the stimuli in the left visual field closer to the centre than they actually were. In the verbal test, underestimation was about 7 deg at the most eccentric position tested (20 deg), and decreased linearly for smaller eccentricities. The effect was similar but less marked in the pointing task. No difference was found for stimuli with luminance or chromatic contrast. Space underestimation was confined to the contralesional space; no evidence of misperception was detected in the ipsilesional hemifield. The present findings are consistent with the view that contralesional space representation is compressed in neglect patients.     

Role of audiovisual synchrony in driving head orienting responses

Many studies now suggest that optimal multisensory integration sometimes occurs under conditions where auditory and visual stimuli are presented asynchronously (i.e. at asynchronies of 100 ms or more). Such observations lead to the suggestion that participants’ speeded orienting responses might be enhanced following the presentation of asynchronous (as compared to synchronous) peripheral audiovisual spatial cues. Here, we report a series of three experiments designed to investigate this issue. Upon establishing the effectiveness of bimodal cuing over the best of its unimodal components (Experiment 1), participants had to make speeded head-turning or steering (wheel-turning) responses toward the cued direction (Experiment 2), or an incompatible response away from the cue (Experiment 3), in response to random peripheral audiovisual stimuli presented at stimulus onset asynchronies ranging from ?100 to 100 ms. Race model inequality analysis of the results (Experiment 1) revealed different mechanisms underlying the observed multisensory facilitation of participants’ head-turning versus steering responses. In Experiments 2 and 3, the synchronous presentation of the component auditory and visual cues gave rise to the largest facilitation of participants’ response latencies. Intriguingly, when the participants had to subjectively judge the simultaneity of the audiovisual stimuli, the point of subjective simultaneity occurred when the auditory stimulus lagged behind the visual stimulus by 22 ms. Taken together, these results appear to suggest that the maximally beneficial behavioural (head and manual) orienting responses resulting from peripherally presented audiovisual stimuli occur when the component signals are presented in synchrony. These findings suggest that while the brain uses precise temporal synchrony in order to control its orienting responses, the system that the human brain uses to consciously judge synchrony appears to be less fine tuned.     

The effects of competition and motor reprogramming on visuomotor selection in unilateral neglect

Patients with unilateral neglect following right hemisphere damage may have difficulty in moving towards contralesional targets. To test the hypothesis that this impairment arises from competing motor programs triggered by irrelevant ipsilesional stimuli, we examined 16 right hemisphere patients, eight with left visual neglect and eight without, in addition to eight healthy control subjects. In experiment 1 subjects performed sequences of movements using their right hand to targets on the contralesional or ipsilesional side of the responding limb. The locations of successive targets in each sequence were either predictable or unpredictable. In separate blocks of trials, targets appeared either alone or with a simultaneous distractor located at the immediately preceding target location. Neglect patients were significantly slower to execute movements to contralesional targets, but only for unpredictable movements and in the presence of a concurrent ipsilesional distractor. In contrast, healthy controls and right hemisphere patients without neglect showed no directional asymmetries of movement execution. In experiment 2 subjects were required to interrupt a predictable, reciprocating sequence of leftward and rightward movements in order to move to an occasional, unpredictable target that occurred either in the direction opposite to that expected, or in the same direction but twice the extent. Neglect patients were significantly slower in reprogramming the direction and extent of movements towards contralesional versus ipsilesional targets, and they also made significantly more errors when executing such movements. Right hemisphere patients without neglect showed a similar bias in reprogramming direction (but not extent) for contralesional targets, whereas healthy controls showed no directional asymmetry in either condition. On the basis of these findings we propose that neglect involves a competitive bias in favour of motor programs for actions directed towards ipsilesional versus contralesional events. We suggest that programming errors and increased latencies for contralesional movements arise because the damaged right hemisphere can no longer effectively inhibit the release of inappropriate motor programs towards ipsilesional events. Received: 1 October 1996 / Accepted: 21 October 1997     

Saccades to the seeing visual hemifield in hemidecorticate patients exhibit task-dependent reaction times and hypometria

In three patients who had one cortical hemisphere removed surgically (hemidecortication), we studied visually-triggered saccades directed contralateral to the intact cortical hemisphere (i.e., ipsilesional saccades). Both saccade reaction times (SRTs) and accuracy of these saccades have been reported as abnormal in hemidecorticate patients, but not monkeys. One explanation for this difference is that deficits in hemidecorticate patients may not have been directly caused by removal of cortical oculomotor structures themselves, but may have been a manifestation of compensatory strategies used to cope with contralesional hemianopia. We hypothesized that deficits in saccade performance to the ipsilesional (seeing) visual hemifield would be directly linked to how easily patients could localize targets in their blind hemifield with searching saccades. To test this hypothesis, we examined how deficits in our patients varied when targets were: (1) randomly presented to either the seeing or blind hemifield for long durations thereby permitting searching saccades in the blind hemifield; (2) presented as in Experiment 1, but briefly flashed thereby removing visual feedback prior to saccade onset thereby rendering searching saccades useless; (3) briefly flashed as in Experiment 2, but at random locations in only the seeing hemifield (blind hemifield irrelevant). Mean SRTs to the seeing hemifield were 165 ms longer than normal in Experiment 2, but only about 40 ms longer in Experiments 1 and 3. Saccade accuracy was characterized by task-dependent hypometria in all three experiments with a mean undershoot of about twice the amplitude variance. The largest undershoots were in Experiments 2 and 3. Our data suggest that deficits resulted from the direct effects of the lesions themselves coupled with context-dependent strategies used to cope with contralesional hemianopia.     

Effectiveness of sensory stimulation on tactile extinction

 Eleven brain-damaged patients with extinction were asked to report double tactile stimuli before, during, and after optokinetic stimulation and transcutaneous electrical stimulation of the posterior neck region. The goal of the study was to test whether tactile extinction is sensitive to these experimental manipulations in order to better understand the nature of the disorder. Both of these sensory stimulations are known to be effective in modulating only higher-order (cognitive) disorders of spatial coding, such as visual hemineglect, deficit of position sense, hemianesthesia, etc. When applied to the side contralateral to the cerebral lesion, both optokinetic and transcutaneous electrical stimulation significantly affected patients’ performances, increasing the amount of detections of contralesional double stimuli. A tendency towards worse performance was observed when sensory stimulation was applied to the ipsilesional side. The reported effectiveness in reducing tactile extinction suggests that the deficit can not be fully ascribed to a peripheral sensory disorder and that it reflects damage to a higher-order cognitive function involved in contralesional space representation or in the deployment of attention to that side of space. The nature of the close relationship between extinction and hemineglect is also discussed from the point of view of extinction as a deficit of space coding. Received: 19 September 1998 / Accepted: 19 February 1999     

Multisensory temporal order judgments: the role of hemispheric redundancy.

Participants made unspeeded 'Which modality came first?' temporal order judgments (TOJs) in response to pairs of auditory and visual stimuli presented at varying stimulus onset asynchronies (SOAs), using the method of constant stimuli. The presentation of auditory and visual stimuli from different spatial positions facilitated performance (i.e. just noticeable differences were lowered) only when the stimuli were presented across the body midline (Experiment 4), but not when both stimuli were either placed on the body midline (Experiments 1-3), or else within the same hemifield (Experiment 5). These results demonstrate that hemispheric redundancy may account for the facilitatory effects reported in previous multisensory TOJs research when stimuli were presented from different spatial locations. Our results also show that the accuracy with which people can make multisensory TOJs is unaffected by the predictability of target stimulus locations, suggesting little role for spatial attention in this aspect of multisensory temporal perception.     

Deficits in feature-based control of attention in a patient with a right fronto-temporal lesion

Three experiments examined feature-based top-down control of search in a patient with right frontal-temporal lobe brain damage (YW), in comparison with normal control participants. In Experiment 1, YW showed normal search functions for single-feature targets. However, he showed abnormal search functions relative to normal control participants when a singleton distractor irrelevant to the target-defining feature was presented. YW showed longer RTs when a target was presented in the contralesional visual field and a singleton distractor was in the ipsilesional visual field (Experiment 1), or when both were presented in the contralesional visual field (Experiment 2). These results suggest that YW's difficulty is due to a failure of selectivity for targets based on top-down control of target-defining features. Experiment 3 compared singleton detection tasks and feature detection tasks. YW showed no deficits on the singleton detection tasks, where no knowledge of target-defining features was required. However, on the feature detection tasks, YW showed long RTs when targets were presented in the contralesional visual field where knowledge of target-defining features was required. We concluded that YW's difficulty in visual search with singleton distractors was due to deficits in feature-based control. We discuss the role of fronto-temporal regions in feature-based control of attention.     

Deficits in feature-based control of attention in a patient with a right fronto-temporal lesion

Three experiments examined feature-based top-down control of search in a patient with right frontal-temporal lobe brain damage (YW), in comparison with normal control participants. In Experiment 1, YW showed normal search functions for single-feature targets. However, he showed abnormal search functions relative to normal control participants when a singleton distractor irrelevant to the target-defining feature was presented. YW showed longer RTs when a target was presented in the contralesional visual field and a singleton distractor was in the ipsilesional visual field (Experiment 1), or when both were presented in the contralesional visual field (Experiment 2). These results suggest that YW's difficulty is due to a failure of selectivity for targets based on top-down control of target-defining features. Experiment 3 compared singleton detection tasks and feature detection tasks. YW showed no deficits on the singleton detection tasks, where no knowledge of target-defining features was required. However, on the feature detection tasks, YW showed long RTs when targets were presented in the contralesional visual field where knowledge of target-defining features was required. We concluded that YW's difficulty in visual search with singleton distractors was due to deficits in feature-based control. We discuss the role of fronto-temporal regions in feature-based control of attention.