Nick Donnelly

Expression is computed separately from facial identity, and it is computed separately for moving and static faces: Neuropsychological evidence

We report data contrasting the processing of facial identity from static photographs, and facial expression from static and moving images, in two patients with face processing impairments. One patient is markedly impaired at perceiving facial identity and he is poor at discriminating facial expression and gender from static photographs of faces. In contrast, he performs normally when required to make judgements of facial expression and gender to faces depicted by sets of moving light dots. The second patient is relatively good at perceiving facial identity, but poor at judging emotional expression from both static and moving faces. The data are consistent with the existence of separate processes for encoding face identity and facial expression, and, furthermore, indicate the separate encoding of expression from moving and static images.

Visual synchrony affects binding and segmentation in perception

The visual system analyses information by decomposing complex objects into simple components (visual features) that are widely distributed across the cortex,. When several objects are present simultaneously in the visual field, a mechanism is required to group (bind) together visual features that belong to each object and to separate (segment) them from features of other objects. An attractive scheme for binding visual features into a coherent percept consists of synchronizing the activity of their neural representations. If synchrony is important in binding, one would expect that binding and segmentation are facilitated by visual displays that are temporally manipulated to induce stimulus-dependent synchrony. Here we show that visual grouping is indeed facilitated when elements of one percept are presented at the same time as each other and are temporally separated (on a scale below the integration time of the visual system) from elements of another percept or from background elements. Our results indicate that binding is due to a global mechanism of grouping caused by synchronous neural activation, and not to a local mechanism of motion computation.

Face processing in high‐functioning adolescents with autism: evidence for weak central coherence

Seventeen adolescents with autism and seventeen typically developing children, matched for chronological age, were tested in a whole versus part paradigm in which participants matched a face target either to a complete face or to a face feature. Previous studies showed an accuracy advantage in whole‐face matching, indicating a holistic processing advantage for adults (Donnelly & Davidoff, 1999). It has been suggested that individuals with autism have difficulty in holistic processing, however the extent to which this difficulty may be moderated by attentional cues is uncertain. The present study included a condition that cued participants to the relevant face feature for matching. In the comparison group, the cue did not moderate the whole‐face matching advantage. In the participants with autism, cueing generated a whole‐face advantage, while uncued stimuli showed no difference between whole face and feature matching. This suggests that a lack of holistic processing in face processing, which is associated with individuals with autism, can be moderated with cueing. The implications for weak central coherence theory are discussed.

The Mental Representations of Faces and Houses: Issues Concerning Parts and Wholes

We explore the integration of facial features and house parts to form holistic representations of complete objects. In Experiments 1, 2, and 3, we test for evidence of the holistic representation of houses and faces. We do so by testing for a complete over part probe advantage (CPA) in 2AFC recognition and matching tasks. We present evidence consistent with holistic features being represented for both types of stimuli. In Experiments 4 and 5, we examine further theeffect with faces. Experiment 4 shows thatfacial features used in the matching task contribute differentially to CPAs across varying probe delays but with a similar pattern to that found in the recognition task (Experiment 1). Experiment5 shows thatCPAs are mandatory and cannot be removed by precueing with the probe type or the name of the feature to be probed.

The cost of search for multiple targets: effects of practice and target similarity

With the use of X-ray images, performance in the simultaneous search for two target categories was compared with performance in two independent searches, one for each category. In all cases, displays contained one target at most. Dual-target search, for both categories simultaneously, produced a cost in accuracy, although the magnitude of this dual-target cost was affected by the nature of the targets. When target feature sets shared values, accuracy in dual-target search was equivalent to that in the less accurate of the two single-target searches. However, when targets comprised different feature sets, accuracy in dual-target search was lower than in either single-target search. These results held after practice. In conclusion, dual-target search performance depends on the target representations required for search. When combined representations contain conflicting values within the most informative feature dimensions, then there is a cost in performance. When target representations share features, the search can be guided by the common values so that resources are not wasted on irrelevant distractors. The implication is that security screener performance might be improved by specializing in searching for threat categories that share features. (PsycINFO Database Record (c) 2009 APA, all rights reserved).

Exploring the function of selective attention and hypervigilance for threat in anxiety

Theoretical frameworks of anxiety propose that attentional biases to threat-related stimuli cause or maintain anxious states. The current paper draws on theoretical frameworks and key empirical studies to outline the distinctive attentional processes highlighted as being important in understanding anxiety. We develop a conceptual framework to make a distinction between two attentional biases: selective attention to threat and hypervigilance for threat. We suggest that these biases each have a different purpose and can account for the typical patterns of facilitated and impaired attention evident in anxious individuals. The framework is novel in its specification of the eye movement behavior associated with these attentional biases. We highlight that selective attention involves narrowing overt attention onto threat to ensure that these stimuli receive processing priority, leading to rapid engagement with task-relevant threat and delayed disengagement from task-irrelevant threat. We show that hypervigilance operates in the presence and absence of threat and involves monitoring for potential dangers via attentional broadening or excessive scanning of the environment with numerous eye movements, leading to improved threat detection and increased distraction from task-irrelevant threat. We conclude that future research could usefully employ eye movement measures to more clearly understand the diverse roles of attention in anxiety.

The impact of Relative Prevalence on dual-target search for threat items from airport X-ray screening

The probability of target presentation in visual search tasks influences target detection performance: this is known as the prevalence effect (Wolfe et al., 2005). Additionally, searching for several targets simultaneously reduces search performance: this is known as the dual-target cost (DTC: Menneer et al., 2007). The interaction between the DTC and prevalence effect was investigated in a single study by presenting one target in dual-target search at a higher level of prevalence than the other target (Target A: 45% Prevalence; Target B: 5% Prevalence). An overall DTC was found for both RTs and response accuracy. Furthermore, there was an effect of target prevalence in dual-target search, suggesting that, when one target is presented at a higher level of prevalence than the other, both the dual-target cost and the prevalence effect contribute to decrements in performance. The implications for airport X-ray screening are discussed.

Developing algorithms to enhance the sensitivity of cancellation tests of visuospatial neglect

We describe a set of algorithms that enhance the sensitivity of cancellation tests used in assessing visuospatial neglect. The algorithms can be readily implemented on a computer and can provide temporal and nontemporal data on strategies used during cancellation. We also present preliminary results from a group of 68 right-hemisphere brain-damaged patients and 12 age-matched control participants, which demonstrate the clinical significance of the measures we have defined.

High or low target prevalence increases the dual-target cost in visual search

Previous studies have demonstrated a dual-target cost in visual search. In the current study, the relationship between search for one and search for two targets was investigated to examine the effects of target prevalence and practice. Color-shape conjunction stimuli were used with response time, accuracy and signal detection measures. Performance was lower in dual-target search compared with the combined performance for two independent single-target searches. The cost in response time slope disappeared with practice, but the cost in accuracy remained. Sensitivity was lower and the decision criterion more conservative in dual-target search than in single-target searches, suggesting that the representation of the target was less effective in dual-target search than in single-target search. Manipulation of target prevalence induced a bias in favor of the more likely correct response: target-present responses were likely under high target prevalence and target-absent responses were likely under low target prevalence. The prevalence effect was greater in dual-target search than single-target search, causing the dual-target cost to be larger under target prevalences that differed from 50%. These findings are important for applied tasks in which targets appear rarely and can differ from each other. For example, the low target prevalence in X-ray security searches may magnify the dual-target cost implicated in previous research with X-ray images (see Menneer, Cave, & Donnelly, 2009). Such a result would increase the need for security personnel to consider alternatives to dual-target search, such as specialization in detecting one target type or training to encourage independent searches for each target.

Nontarget objects can influence perceptual processes during object recognition

Previous experiments have shown that objects are recognized more readily in a semantically consistent visual context. However, the benefit from context could be explained by response bias, and may not reflect the influence of context on the perceptual processes of recognition. We conducted a six-alternative forced-choice experiment to measure semantic and perceptual errors. A target object appeared briefly, surrounded by four context objects. The target was more accurately identified when the context consisted of objects semantically related to the target. The large number of semantic errors, which increased when the context presentation preceded the target, showed that response bias did account for a proportion of the context effect. Nevertheless, significant facilitation was still present after a bias correction. Recognition of an object can be affected by context not only when it is embedded in a coherent naturalistic scene, but also when it is simply near other related objects. Materials associated with this article may be accessed at www.psychonomic.org/archive.