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  • Dissociation between decoding and reasoning about mental states in patients with theory of mind reasoning impairments.

    3 July 2018

    Theory of mind (ToM) reasoning may involve a multiplicity of processes, including an initial stage, where cues relevant for social processes are detected and decoded, and a mentalizing stage, where the decoded information is used to reason about mental states. Here we report that the processing of lower-order facial cues relevant to social judgments can be relatively spared in patients with impaired ToM reasoning. We discuss the implications for understanding the mechanisms underlying social judgments in brain-lesioned patients.

  • Automatic guidance of attention from working memory.

    3 July 2018

    Recent research has shown interactions between the process of keeping information 'online' in working memory, and the processes that select relevant information for a response. In particular, our ability to select stimuli in the environment can be modulated by whether the stimuli match the current contents of working memory. Guidance of selection from working memory occurs automatically, even when it is detrimental to performance. Neurophysiological data, from functional brain imaging, indicate that the interaction between working memory and attention is based on neuronal mechanisms distinct from the processes mediating 'bottom-up' priming effects from implicit memory. We discuss the importance of 'top-down' influences from working memory on the 'early' deployment of attention and on the processes that gate visual information into awareness.

  • Automatic statistical processing of visual properties in simultanagnosia.

    3 July 2018

    Previous research has suggested that, when operating in a distributed attention mode, the visual system automatically represents visual displays by their overall statistics, rather than their individual properties. Recent neuropsychological work shows partly preserved distributed attention in simultanagnosic patients, who are typically defined as only perceiving one object at a time. Here we assessed whether GK, a patient with simultanagnosia, shows averaging of stimulus properties when distributing his attention across a set of items. We manipulated different stimulus properties in two experiments: color shades and size. We found that, when GK was in a distributed mode of attention, he (incorrectly) identified the mean object from two classes of exemplars more than in a control condition, when only one exemplar class was present. Overall, this study suggests that automatic statistical processing of color and size is possible in simultanagnosia.

  • Contrasting effects of repetition across tasks: implications for understanding the nature of refractory behavior and models of semantic memory.

    3 July 2018

    We describe a patient (J.M.) who showed "refractory" behavior in picture-word matching tasks--that is, his performance became poorer when items were repeated. This contrasts with the facilitatory effects of repetition usually observed in normal participants. We show for the first time that there can be facilitatory effects of repetition on some tasks, even though refractory behavior is shown on the same items in other tasks. In particular, in Experiments 1 and 2, we demonstrate that J.M. showed contrasting effects of repetition across different components of the language system: There were facilitatory effects of repetition priming on lexical decision but refractory behavior on picture-word matching. In Experiments 3 and 4, we demonstrate that J.M. showed contrasting effects of repetition within the same system (semantic memory). His performance became refractory when items were repeated in picture-word matching (Experiment 3), but it was facilitated when items were repeated in superordinate categorization (Experiment 4). These contrasting patterns of facilitation and interference from repetition priming have implications for understanding the nature of refractory behavior and for constraining theoretical accounts of semantic memory.

  • The representation of unseen objects in visual neglect: effects of view and object identity.

    3 July 2018

    We provide evidence for long-term priming based on view-specific representations of neglected stimuli. A patient with visual neglect, M.P., was asked to search for a target presented amongst other objects on a table. Subsequently recognition memory was tested for items that were identified and for items missed in search. Items that were missed were rejected more slowly than novel items in the recognition memory task, providing evidence for implicit processing (Experiment 1). Implicit memory for missed items was both item-specific (Experiment 2) and view-specific (Experiment 3), and it was eliminated when there were intervening activities lasting about 1 hour (Experiment 4). There was also an implicit memory for distractors in the search task, which was item- but not view-specific (Experiments 2 and 3) and it lasted for at least an hour, even with other intervening activities (Experiment 4). The data suggest that the representations of neglected stimuli may differ qualitatively from those of nonneglected items, with representations of neglected objects being both view-specific and vulnerable across extended retention intervals. The results support the argument that attention is needed in order to encode object representations that are robust to view transformations and temporal decay or interference.

  • Global processing of compound letters in a patient with Balint's syndrome

    3 July 2018

    We report data on the ability of a patient with Balint's syndrome (GK) to process global information from compound letters. As with other patients with Balint's syndrome, GK was impaired at responding to large, global letters. In Experiment 1 we show that this was due to local capture rather than the absolute size of the stimuli. Also, despite his impairment with global letters, GK showed global interference on local judgements, indicating that some implicit processing took place at the global level. Interestingly, the inability to perceive large global letters was overcome when GK identified a solid, large prime letter prior to the onset of the compound figure (Experiment 2). This priming effect was temporary, and decreased as the interval between the prime and the compound letter increased (Experiment 3). When the prime was an English letter, the effect was maintained even when GK only had to identify the prime's colour, provided a colour-identification block of trials followed rather than preceded a block of trials where prime shapes had to be identified (Experiment 4). In contrast, there was no priming when GK had to identify the colour of English letter primes in a trial block following a block where the task was to identify the colour of Hebrew letter primes (Experiment 5). Overall the data indicate that local capture in Balint's syndrome can be overcome by actively priming a wide attentional window. The results can be interpreted in terms of an interaction between spatial attention and grouping processes that subserves the perception of global compound letters. © 2005 Psychology Press Ltd.

  • Can segregation within the semantic system account for category-specific deficits?

    3 July 2018

    Functional neuroimaging was used to investigate the extent to which category-specific semantic deficits in patients can be accounted for in terms of the demands placed on neural systems underlying different types of semantic knowledge. Unlike previous functional imaging studies of category specificity, we used a factorial design that crossed category (tools and fruits) with tasks requiring retrieval of either action or perceptual (real life size) knowledge. The presentation of tools relative to fruit increased activation in the same left posterior middle temporal area that was linked to the retrieval of action knowledge in general (for fruit as well as tools). However, we found no correlation between activation evoked by fruit and the size retrieval task. The left medial anterior temporal cortex was the only region to be activated for fruit relative to tools. We argue that the sensory-functional theory of category-specific effects is insufficient to account for the current neuroimaging literature. However, the data do support a more refined version of the theory: tools, relative to fruit, are more strongly linked to manipulative/motor knowledge and, for some tasks, fruit may be more reliant on integrating multiple semantic features.

  • Top down modulation of attention to food cues via working memory.

    3 July 2018

    Attentional biases towards food cues may be linked to the development of obesity. The present study investigated the mechanisms underlying attentional biases to food cues by assessing the role of top down influences, such as working memory (WM). We assessed whether attention in normal-weight, sated participants was drawn to food items specifically when that food item was held in WM. Twenty-three participants (15 f/8 m, age 23.4±5 year, BMI 23.5±4 kg/m(2)) took part in a laboratory based study assessing reaction times to food and non-food stimuli. Participants were presented with an initial cue stimulus to either hold in WM or to merely attend to, and then searched for the target (a circle) in a two-item display. On valid trials the target was flanked by a picture matching the cue, on neutral trials the display did not contain a picture matching the cue, and on invalid trials the distractor (a square) was flanked by a picture matching the cue. Cues were food, cars or stationery items. We observed that, relative to the effects with non-food stimuli, food items in WM strongly affected attention when the memorised cue re-appeared in the search display. In particular there was an enhanced response on valid trials, when the re-appearance of the memorised cue coincided with the search target. There were no effects of cue category on attentional guidance when the cues were merely attended to but not held in WM. These data point towards food having a strong effect on top-down guidance of search from working memory, and suggest a mechanism whereby individuals who are preoccupied with thoughts of food, for example obese individuals, show facilitated detection of food cues in the environment.

  • Flexible feature-based inhibition in visual search mediates magnified impairments of selection: evidence from carry-over effects under dynamic preview-search conditions.

    3 July 2018

    Evidence for inhibitory processes in visual search comes from studies using preview conditions, where responses to new targets are delayed if they carry a featural attribute belonging to the old distractor items that are currently being ignored-the negative carry-over effect (Braithwaite, Humphreys, & Hodsoll, 2003). We examined whether inhibition was applied in the same manner across different types of displays or whether the inhibitory weighting applied to different features varied with their utility for the search task. To test this, we present the first empirical investigation of negative carry-over effects under the ecologically valid conditions of dynamic visual search. Experiment 1 investigated preview search using dynamic moving and static displays. Detection was very poor when new targets carried the color of the old distractors, and this negative carry-over effect was significantly exaggerated with moving, compared with static, displays. Experiments 2a and 2b demonstrated that this effect could not be attributed to an increased role of preattentive grouping between new and old items for dynamic displays. Collectively, the findings suggest that feature-based inhibition contributes strongly to preview search through dynamic displays, and this leads to an amplified attentional blindness to new targets. The data specifically indicate that inhibitory processes in search differentially weight color and location in moving and static displays, and that feature-based inhibition may underlie many instances of sustained inattentional blindness in everyday life.

  • Spreading suppression and the guidance of search by movement: evidence from negative color carry-over effects.

    3 July 2018

    A growing number of studies have shown that significant impairments to search and selection can occur if the target item carries a feature of the irrelevant distractors currently being ignored Braithwaite, Humphreys, and Hodsoll (Journal of Experimental Psychology: Human Perception and Performance, 29, 758-778, 2003). However, these effects have been documented only when search has been extended over time (i.e., in preview search), and not in standard search displays with simultaneously presented items. Here, we present the first evidence that similar costs to selection can occur in simultaneous displays under appropriate circumstances. In the present experiment, participants searched a display for a moving target letter among static and moving distractors. Search efficiency was significantly enhanced for a moving target when half of the letters moved (and half remained static), allowing the static items to be excluded from search. However, if the moving target then shared its color with the irrelevant static items, significant costs emerged, relative to baselines. These results are consistent with the involvement of a general feature-based suppression mechanism in selection, operating over space as well as time.