Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Types of interference and their resolution in monolingual language production

There is accumulating evidence that speakers recruit inhibitory control to manage the conflicting demands of online language production, e.g., when selecting from among co-activated representations during object naming or when suppressing alternative competing terms in referential language use. However, little is known about the types of conflict resolution mechanisms underlying the production processes. The aim of this research was to assess the relative contribution of various forms of interference arising at different stages of information processing as well as their control to single- and multi-word utterance production. The systematic review of picture-word interference (PWI) studies (Study 1) was conducted to trace the origins of semantic context effects in order to address the question of whether spoken word production can be seen as a competitive process. The various manipulations of PWI task parameters in the reviewed studies produced a mixture of findings that were either contradictory, unable to discriminate between the rival theories of lexical access, or of questionable validity. Critically, manipulations of distractor format and of whole-part relations with varied association strength produced sufficiently strong evidence to discount post-lexical non-competitive accounts as the dominant explanations for observed interference effects, constraining their locus to early rather than late processing stages. The viability of competitive hypotheses was upheld; however, this is contingent on the relative contribution of pre-lexical processes, which remains to be confirmed by future research. The relative contribution of different conflict resolution mechanisms (measured by the anti-saccade, arrow flanker and Simon arrow tasks) to object naming under prepotent (the PWI task) and underdetermined competition (picture naming task with name agreement, NA, manipulation) was further investigated in Study 2, while Study 3 extended the notion of separability of the inhibitory processes to grammatical encoding (grammatical voice construction and number agreement computation). In Study 2, only the flanker effect was a significant predictor of the PWI but not NA effect, while the remaining inhibitory measures made no significant contribution to either the PWI or NA effect. Participants with smaller flanker effects, indicative of better resolution of representational conflict, were faster to name objects in the face of competing stimuli. In Study 3, only utterance repairs were reliably predicted by the flanker and anti-saccade effects. Those who resolved representational conflict or inhibited incorrect eye saccades more efficiently were found to self-correct less often during online passive voice construction than those with poorer resolution of inhibition at the representational and motor output level. No association was found between the various inhibitory measures and subject-verb agreement computation. The negative priming study with novel associations (Study 4) was an attempt at establishing the causal link between inhibition and object naming, and specifically whether inhibition that is ostensibly applied to irrelevant representations spreads to its associatively related nodes. Response times to the associated probe targets that served as distractors in previous prime trials were no different than response times to non-associated probe targets. Possible explanations are discussed for the lack of the associative negative priming effect. The studies described here implicate two types of interference resolution abilities as potential sources of variability in online production skills, with the underlying assumption that better resolution of conflict at the representational and motor output level translates to faster naming and more fluent speech. There is insufficient evidence to determine whether the representational conflict is lexical or conceptual in nature, or indeed whether it is inhibitory in the strict sense. It also remains to be established whether interference that likely ensues at the response output stage is due to some criterion checking process (self-monitoring), recruitment of an inhibitory mechanism (response blocking) or both

Dynamic weighting of feature dimensions in visual search: behavioral and psychophysiological evidence

Dimension-based accounts of visual search and selection have significantly contributed to the understanding of the cognitive mechanisms of attention. Extensions of the original approach assuming the existence of dimension-based feature contrast saliency signals that govern the allocation of focal attention have recently been employed to explain the spatial and temporal dynamics of the relative strengths of saliency representations. Here we review behavioral and neurophysiological findings providing evidence for the dynamic trial-by-trial weighting of feature dimensions in a variety of visual search tasks. The examination of the effects of feature and dimension-based inter-trial transitions in feature detection tasks shows that search performance is affected by the change of target-defining dimensions, but not features. The use of the redundant-signals paradigm shows that feature contrast saliency signals are integrated at a pre-selective processing stage. The comparison of feature detection and compound search tasks suggests that the relative significance of dimension-dependent and dimension-independent saliency representations is task-contingent. Empirical findings that explain reduced dimension-based effects in compound search tasks are discussed. Psychophysiological evidence is presented that confirms the assumption that the locus of the effects of feature dimension changes is perceptual pre-selective rather than post-selective response-based. Behavioral and psychophysiological results are considered within in the framework of the dimension weighting account of selective visual attention

The Behavioral and Electrophysiological Effects of Discrimination and Inhibition Training on Visual Selective Attention: an ERP and Time-Frequency Analysis

Enhancement of task relevant information and the suppression of task irrelevant information are the two co-occurring mechanisms of selective attention. Studies have shown that ERP components (specifically N2, P3, and RP) and the alpha band (8-14 Hz) rhythm correspond to neural mechanisms and processes of visual selective attention, especially conflict resolution. Tested by a modified version of the visual flanker task, a conflict task employing inhibitory control, two groups of healthy adults were exposed to three weeks of cognitive training; either discrimination training (trained to discriminate target orientation) or inhibition training (trained to ignore interfering distractors) to investigate whether training impacts behavioral and neural correlates associated with stimuli processing. Behavioral analysis revealed a reduction in both Garner interference [F(1,33)=6.85, p=0.01] and Congruity effect [F(2,66)= 4.35, p=.02] after inhibition training, indicating better conflict resolution. Neural analyses revealed that the amplitude of N2 to target stimuli increased equally for both congruent and incongruent trials, albeit to a larger degree after inhibition training compared to discrimination training [F(1,32)= 5.18, pF(1,32)= 5.69, pF(1,32)= 4.87,

Top-down modulation of task features in rapid instructed task learning: An ERP study

Rapid instructed task learning (RITL) is the ability to quickly restructure behaviour into new configurations based on explicit instruction (Cole, Laurent, & Stocco, 2012). The majority of RITL research has been dominated by neuroimaging studies, which suggest unique involvements of the lateral prefrontal cortex and the posterior parietal cortex, although the exact mechanisms of RITL execution remain poorly understood. The electrophysiological responses of 22 adults undergoing a computerised RITL sequential dependency task were obtained, with the expectation that task relevance processes would be observable at posterior N1, anterior P2a/N2, and central P3b. Early top-down amplitudinal modulation was found in N1 for all item types, and this was related to non-target N2 amplitudes, with both time windows showing preliminary support for compositionality of individual task components. Evidence for compositionality in attentional template matching processes was also found in the P2a/N2 complex. Central P3b did not appear to be involved in task relevance processes per se, perhaps being more involved in attentional resource allocation. These findings answer important questions as how to task-relevant feature identification and task component sequencing occur in RITL

Shared mechanisms support controlled retrieval from semantic and episodic memory: Evidence from semantic aphasia

Semantic cognition is supported by at least two interactive components: semantic representations and control mechanisms that shape retrieval to suit the circumstances. Semantic and episodic memory draw on largely distinguishable stores, yet it is unclear whether controlled retrieval from these representational systems is supported by shared mechanisms. Patients with semantic aphasia (SA) show heteromodal semantic control deficits following stroke to left inferior frontal gyrus (LIFG), an area implicated in semantic processing plus the control of memory and language. However, episodic memory has not been examined in these patients and although the role of LIFG in semantics is well-established, neuroimaging cannot ascertain whether this area is directly implicated in episodic control or if its activation reflects semantic processing elicited by the stimuli. Neuropsychology can address this question, revealing whether this area is necessary for both domains. We found that: (i) SA patients showed difficulty discarding dominant yet irrelevant semantic links during semantic and episodic decisions. Similarly, recently encoded events promoted interference during retrieval from both domains. (ii) Deficits were multimodal (i.e. equivalent using words and pictures) in both domains and, in the episodic domain, memory was compromised even when semantic processing required by the stimuli was minimal. (iii) In both domains, deficits were ameliorated when cues reduced the need to internally constrain retrieval. These cues could involve semantic information, self-reference or spatial location, representations all thought to be unaffected by IFG lesions. (iv) Training focussed on promoting flexible retrieval of conceptual knowledge showed generalization to untrained semantic and episodic tasks in some individuals; in others repetition of specific associations gave rise to inflexible retrieval and overgeneralization of trained associations during episodic tasks. Although the neuroanatomical specificity of neuropsychology is limited, this thesis provides evidence that shared mechanisms support the controlled retrieval of episodic and semantic memory

Preserved Extra-Foveal Processing of Object Semantics in Alzheimer’s Disease

Alzheimer’s disease (AD) patients underperform on a range of tasks requiring semantic processing, but it is unclear whether this impairment is due to a generalised loss of semantic knowledge or to issues in accessing and selecting such information from memory. The objective of this eye-tracking visual search study was to determine whether semantic expectancy mechanisms known to support object recognition in healthy adults are preserved in AD patients. Furthermore, as AD patients are often reported to be impaired in accessing information in extra-foveal vision, we investigated whether that was also the case in our study. Twenty AD patients and 20 age-matched controls searched for a target object among an array of distractors presented extra-foveally. The distractors were either semantically related or unrelated to the target (e.g., a car in an array with other vehicles or kitchen items). Results showed that semantically related objects were detected with more difficulty than semantically unrelated objects by both groups, but more markedly by the AD group. Participants looked earlier and for longer at the critical objects when these were semantically unrelated to the distractors. Our findings show that AD patients can process the semantics of objects and access it in extra-foveal vision. This suggests that their impairments in semantic processing may reflect difficulties in accessing semantic information rather than a generalised loss of semantic memory