James Danckert

Common Mechanisms in Perception and Action: Attention and Performance XIX: Wolfgang Prinz, Bernhard Hommel (Eds.), Oxford University Press, 2002, Price: £ 65.00, ISBN: 0-19-851069

The latest volume in the Attention and Performance series, Common Mechanisms in Perception and Action, represents a comprehensive review of current thinking on how perceptions and actions can be integrated. Only in recent times have we been able to speak of ‘perception’ and ‘action’ in the same breath, but often with a distinct focus on how the two can be dissociated. In contrast, this volume showcases the current thinking on how processes involved in perception and action are integrated to form what appear to be seamless behaviours. The format of the current volume differs somewhat from its predecessors with each of the five sections beginning with a brief introduction, followed by a longer chapter denoted as a tutorial on a particular aspect of the perception-action literature, from space and time perception to action imitation and the co-ordination and integration of perceptions and actions. Each tutorial is then followed by shorter articles that address more specific questions and issues relevant to that section. It is impossible to do justice to the many outstanding contributions to this volume in a short review. Instead, I intend to focus on a theme that I felt was apparent throughout the volume—namely that temporal processing and body schemas play a vital role in integrating actions and perceptions. Suffice to say that with excellent contributions from Bruce Bridgeman, Patrick Haggard, Umberto Castiello, Vittorio Gallese, Pierre Jolicœur and many others, this volume is an essential and comprehensive reference for all scientists interested in the complex interactions between our perceptions and the control of actions. The Association Lecture for this series was delivered by Sylvan Kornblum who for the past 20 years or so has developed a comprehensive model describing the relationship between stimuli and their associated responses (the dimensional overlap model). This model is perhaps the most comprehensive attempt at addressing the common mechanisms of perception and action. Admittedly, there is a risk of confusing rather than clarifying our understanding of stimulus–response properties as the model fractionates the ways in which they can be described (with now up to 12 different task classifications!). However, in this chapter, Kornblum and Stevens address only four of the task types and specifically draw attention to the effect that repetition of either stimulus or response properties has on performance. Their suggestion that such repetitions reduce information processing load thereby leading to faster processing is perhaps not surprising. However, they call attention to an important theme that recurs throughout the volume— namely, consideration of the temporal properties of actions and perceptions. Rather than focusing on the distinctions to be made between perception and action, exploration of the temporal nature of both processes allows us to speculate on how they might interact. Rossetti and Pisella address this possibility directly in their tutorial and suggest that actions can be driven by object representations in either the dorsal or ventral streams, depending on the temporal constraints of the task. They describe work on an optic ataxic patient who shows deficient on-line control of actions due to dorsal stream damage, but when given enough time to develop an action plan through alternative routes, presumably in the ventral stream, can perform quite well. In this sense, temporal constraints of a task may determine which neural pathway is engaged for a given behaviour—and this theme recurs in other chapters of the book. Rossetti and Pisella also briefly discuss work on a patient who demonstrated residual somatosenory processing despite hemisensory impairments. They call this ‘action-numbsense’ drawing the analogy between their patient’s residual functions and blindsight. Importantly, the patient’s residual functions are best when tested immediately or after a short delay ( <1 s), as is also the case for blindsight patients. Again this highlights the temporal constraints on actions and perceptions, but also draws our attention to the role played by body schemas in action/perception interactions. In other chapters, imitation of the actions of others, mirror neurons and the analysis of biological motion all highlight the importance of body schemas in perception and action. It is perhaps these two elements, temporal processing and body schemas, that act as the glue in mediating between our perceptions and actions. In that context, perhaps it is through our most challenging neuropsychological cases that we can explore the interactions between action and perception as mediated by both temporal constraints and body schema. For example, patients with the disorder of unilateral neglect may represent an ideal avenue through which these issues can be explored. We know the disorder is not one of impaired low-level perception, nor does it obviously reflect deficient control of actions in the same way that apraxia does. Yet these patients are completely unaware of stimuli and events

Revisiting unilateral neglect.

Unilateral neglect, a neurological disorder in which patients fail to detect or respond to contralesional stimuli, has long been considered a failure of attentional orienting mechanisms. This review provides a selective overview of the prominent biases in spatial orienting and exploratory motor behaviour observed in these patients before considering the impact of other factors on the presentation of the disorder and how those factors might inform current neurological models of neglect. In the latter part of the review, we intend to suggest that neglect is likely to be a combination of distinct but interacting impairments including biases in attentional orienting, exploratory motor behaviours and a deficit of spatial working memory. That is, we suggest that the cardinal symptom of neglect - a loss of awareness for contralesional stimuli and events - arises as a result of a combination of these impairments rather than being associated solely with the more dramatic and immediately evident biases in spatial attention.

Eye movements tell only half the story

The dramatic improvements of neglect symptoms after prism adaptation (PA) have been interpreted as evidence that PA reorganizes higher levels of spatial representation. Here the authors demonstrate that while the exploratory eye movements of a patient with neglect were clearly shifted toward the left after PA, he still showed no awareness for the left side of the stimuli he was now actively exploring. PA modulates functions of the parietal lobe, such as eye movement control, but fails to influence the underlying mechanisms of neglect.

Spatiotemporal distribution of facilitation and inhibition of return arising from the reflexive orienting of covert attention

Currently, there is debate regarding both the spatial and temporal relationship between facilitation and inhibition of return (IOR) components of attention, as observed on the covert orienting of visual attention task (COVAT). These issues were addressed in a series of experiments where the spatial and temporal relationships between cue and target were manipulated. Facilitation occurred only when the stimulus onset asynchrony (SOA) was short and there was temporal overlap between cue and target. IOR occurred only when SOA was long and there was no temporal overlap between cue and target. Facilitation encompassed the cued location and all locations between the cue and fixation, whereas IOR arose for the entire cued hemifield. These findings suggest that the facilitation and IOR found on COVATs that use noninformative peripheral cues are separable and stimulus-driven processes.

Attention, motor control and motor imagery in schizophrenia: implications for the role of the parietal cortex.

Many recent models of schizophrenia have attempted to explain the so-called first-rank symptoms in terms of a breakdown in the self-monitoring of thoughts and behaviours. These models have focused on the most common symptom of schizophrenia auditory hallucinations-suggesting that they may represent disordered self-monitoring of internal speech. As such, much attention has been given to the role of the temporal and frontal cortices in the clinical presentation of patients with schizophrenia. In this review, we examine the role of the posterior parietal cortex (PPC) in schizophrenia within the context of recent models of self-monitoring deficits in these patients. Attentional dysfunctions and certain impairments of motor control and motor imagery all point towards the involvement of the parietal cortex in the disorder. In particular, we suggest that patients experiencing passivity phenomena (e.g., delusions of control) may have particular impairments of parietal function related to poor utilisation of forward models of intended actions. We also present a novel hypothesis that suggests differential impairments of the left and right parietal cortices in schizophrenia may help explain many of the first-rank symptoms of the disorder.

Neglected Time: Impaired Temporal Perception of Multisecond Intervals in Unilateral Neglect

Recent neuroimaging and neuropsychological studies have suggested that the right hemisphere, particularly frontal regions, is important for the perception of the passage of time. We examined the ability to estimate durations of up to 60 sec in a group of eight patients with unilateral neglect. When estimating multisecond intervals, neglect patients grossly underestimated all durations. On average, healthy controls (HC) demonstrated reasonably accurate estimates of all durations tested. Although the right hemisphere lesioned control patients without neglect also tended to underestimate durations, these underestimations were significantly better than the performance of the neglect group. These findings suggest a pivotal role for a right hemisphere fronto-parietal network in the accurate perception of multisecond durations. Furthermore, these findings add to a growing body of literature suggesting that neglect cannot be understood simply in terms of a bias in orienting attention to one side of space. Additional deficits of the kind demonstrated here are likely to be crucial in determining the nature and extent of the loss of conscious awareness for contralesional events.

Facilitation and inhibition arising from the exogenous orienting of covert attention depends on the temporal properties of spatial cues and targets.

On the covert orienting of visual attention task (COVAT), responses to targets appearing at the location indicated by a non-predictive spatial cue are faster than responses to targets appearing at uncued locations when stimulus onset asynchrony (SOA) is less than approximately 200 ms. For longer SOAs, this pattern reverses and RTs to targets appearing at uncued locations become faster than RTs to targets appearing at the cued location. This facilitation followed by inhibition has been termed the biphasic effect of non-predictive peripheral spatial cues. Currently, there is debate about whether these two processes are independent. This issue was addressed in a series of experiments where the temporal overlap between the peripheral cue and target was manipulated at both short and long SOAs. Results showed that facilitation was present only when the SOA was short and there was temporal overlap between cue and target. Conversely, inhibition occurred only when the SOA was long and there was no temporal overlap between cue and target. The biphasic effect, with an early facilitation followed by a later inhibition, occurred only when the cue duration was fixed such that there was temporal overlap between the cue and target at short but not long SOAs. In a final experiment, the duration of targets the temporal overlap between cue and target and the SOA were manipulated factorially. The results showed that facilitation occurred only when the SOA was short, there was temporal overlap between cue and target and the target remained visible until the subject responded. These results suggest that the facilitation and inhibition found on COVATs which use non-informative peripheral cues are independent processes and their presence and magnitude is related to the temporal properties of cues and targets.

Neuropsychological Profile of Acute Alcohol Intoxication during Ascending and Descending Blood Alcohol Concentrations

Numerous studies have investigated the effects of alcohol on motor processes during rising and declining blood alcohol concentrations (BAC), however, relatively little research has examined the alcohol-induced impairment of cognitive performance on the two limbs of the BAC curve. This experiment administered a neuropsychological test battery to assess the degree to which rising and declining BACs during an acute dose of alcohol impair nine cognitive processes within an individual. In all, 20 healthy male social drinkers (university students) were assigned to one of two groups (n=10) who received a beverage containing either 0.0 g/kg (placebo) or 0.65 g/kg alcohol and performed the test battery when BAC was increasing and was decreasing. Comparisons of alcohol and placebo groups revealed impairment (slower response and/or increased errors) in seven of the cognitive processes: long-term verbal memory; information processing; declarative memory; inhibitory control; short-term visual memory; long-term visual memory, and visual-spatial working memory. However, some processes were impaired only during rising BACs whereas the impairment of others during declining BACs was evident only by an increase in errors. These results show cognitive tasks performed by an individual are not similarly affected by rising and declining BACs, and call attention to the importance of assessing both speed and accuracy on both limbs of the BAC curve. The particular cognitive processes differentially affected by rising vs declining BACs raised the possibility that acute alcohol intoxication may impair one cerebral hemisphere to a greater degree than the other, and this could be explored by neuroimaging techniques.

Direct effects of prismatic lenses on visuomotor control: an event-related functional MRI study

Exposure to prisms has long been used to explore the control of visually guided actions primarily because adaptation requires the recalibration of misaligned reference frames due to perturbed visual input (i.e. eye‐in‐head and hand‐centered reference frames must be realigned). To date, the only neuroimaging study to explore the direct effects of prisms on pointing used positron emission tomography and found increased activation only in right parietal cortex. We used event‐related functional MRI to examine the effects of prisms on visuomanual pointing. Results demonstrated changes in activity in the anterior cingulate, the anterior intraparietal region and in a medial region of the right cerebellum. Specifically, activity in these regions was higher for the first few pointing trials made while viewing targets through prisms when directly contrasted to the last few trials. These results highlight that a more extensive network of cortical and cerebellar regions is involved in recalibrating visuomotor commands in the face of perturbed visual input.

Selective, Non-lateralized Impairment of Motor Imagery Following Right Parietal Damage

Using variants of a visually guided pointing task, in which subjects make pointing movements towards targets of varying sizes, we explored motor imagery in a patient with visual neglect. When this patient actually pointed towards targets of different sizes he showed the normal correlation between movement duration (MD) and target size, such that MD increased as target size decreased. In contrast, his imagined movements did not show the same speed-accuracy trade-off observed for actual movements. This was true regardless of the hand used or the initial direction of movement (left versus right). The patient performed normally on several tasks of visual imagery, including size estimation, perceptual discrimination and localization of cities on an imagined map. This patient’s performance suggests that the networks in the right parietal lobe play an important role in the generation of internal models of motor movements regardless of the hand used to perform the task.