Straight after the turn: the role of the parietal lobes in egocentric space processing.

Spatial information processing with respect to an egocentric reference frame has been shown to recruit a fronto-parietal network along the dorsal stream. The present study investigates how brain lesions in the relevant areas affect the ability to navigate through computer-simulated tunnels shown from a first person perspective. Our results suggest that parietal, but not frontal, patients are impaired in this task.

The redundant-signals paradigm and preattentive visual processing.

Physiological and cognitive models of vision agree that the pre-attentive processing of visual stimuli is organized in a parallel and segregated fashion. However, several incompatible models have been proposed for the subsequent processing stages. They differ in their assumptions about architecture (serial, parallel, or coactive/integrative), stopping-rules (self-terminating, or exhaustive), spatial specificity of saliency signal coding (signal pooling across locations, or spatially distinct processing), and dependency of target detection on the prior allocation of attention (pre-attentive, or post-selective).

Electrophysiological markers of visual dimension changes and response changes.

In cross-dimensional visual search tasks, target discrimination is faster when the previous trial contained a target defined in the same visual dimension as the current trial. The dimension-weighting account (DWA; A. Found & H.

Top-down inhibition of search distractors in parallel visual search.

In three experiments, we examined distractor inhibition in parallel ("pop-out") visual search. Distractor inhibition was measured in terms of reaction time (RT) to a simple luminance increment probe presented, after the search task response, at display locations that either contained a search distractor (on-probe) or were blank (off-probe). When the search stimuli remained in view, the on-probe (relative to off-probe) RT cost was larger than in a baseline condition in which observers had only to passively view, rather than search, the display.

The contrasting impact of global and local object attributes on Kanizsa figure detection.

Studies on the involvement of object completions in search for illusory figures have so far reported equivocal results. We have addressed this issue by investigating at which level object attributes in Kanizsa figures influence search. Employing a paradigm that investigated global and local attributes in the composition of distractors with relation to target composition, we report a selective involvement of multilevel processing upon detection.

Searching for two feature singletons in the visual scene: the localized attentional interference effect.

The localized attentional interference (LAI) effect was investigated in a visual search task requiring participants to simultaneously monitor two spatially separated features from the same or different dimensions. In Experiment 1, the search type was blocked and targets were defined by fixed feature values in two dimensions (e.g.

Attentional resources and pop-out detection in search displays.

Detecting pop-out targets is often considered as a fast, spontaneous and preattentive process. In most experimental studies, however, the observer's attention is explicitly focused on the detection task. We investigated pop-out detection under varying attention conditions: when pop-out displays were (a) not attended and not relevant, (b) attended and relevant and (c) could be attended but were not relevant.

The capacity of attention and simultaneous perception of objects: a group study of Huntington's disease patients.

Using a whole report-paradigm based on [Bundesen, C. (1990). A theory of visual attention.

What do eye movements reveal about the role of memory in visual search?

Horowitz and Wolfe (1998, 2003) have challenged the view that serial visual search involves memory processes that keep track of already inspected locations. The present study used a search paradigm similar to Horowitz and Wolfe's (1998), comparing a standard static search condition with a dynamic condition in which display elements changed locations randomly every 111 ms. In addition to measuring search reaction times, observers' eye movements were recorded.

Closure of salient regions determines search for a collinear target configuration.

Grouping operations offer an effective mechanism by which to structure complex visual scenes. Among the various principles that support element integration, closure may be regarded as a main factor in shape extraction. In five experiments, we investigated the impact of grouping by closure on search for target configurations made up of collinearly arranged corner junctions.

Brain electrical correlates of dimensional weighting: an ERP study.

In visual search, there is a reaction time (RT) cost for targets on a given trial if the previous target was defined in a different dimension. According to the "dimension-weighting" account (Müller, Heller, & Ziegler, 1995), limited attentional weight needs to be shifted to the new dimension, resulting in slower RTs. The present study aimed at identifying brain electrical correlates associated with the weight shift.

Detecting pop-out targets in contexts of varying homogeneity: investigating homogeneity coding with event-related brain potentials (ERPs).

Searching for a target among many distracting context elements might be an easy or a demanding task. Duncan and Humphreys (Duncan, J., Humphreys, G.

Cross-trial priming in visual search for singleton conjunction targets: role of repeated target and distractor features.

Kristjánsson, Wang, and Nakayama (2002) demonstrated that visual search for conjunctively defined targets can be substantially expedited ("primed") when target and distractor features are repeated on consecutive trials. Two experiments were conducted to examine whether the search response time (RT) facilitation on target-present trials results from repetition of target-defining features, distractor features, or both. The experiments used a multiple conjunctive search paradigm (adapted from Kristjánsson et al.

Electrophysiological correlates of similarity-based interference during detection of visual forms.

Illusory figure completion demonstrates the ability of the visual system to integrate information across gaps. Mechanisms that underlie figural emergence support the interpolation of contours and the filling-in of form information [Grossberg, S., & Mingolla, E.

Visual search for size-defined target objects is modulated by the Ebbinghaus apparent-size illusion: facilitatory and inhibitory effects of the context objects.

Five experiments were carried out to investigate under which conditions the apparent size of objects is computed and exploited optimally in visual search for size-defined targets. Observers searched for a target test circle that was retinally larger than the distractor test circles, with both types of circles surrounded by context circles modulating the apparent size of the test circles (Ebbinghaus illusion). RTs were the faster the better test circles could be differentiated from the context circles, ie with smaller numbers of context circles, larger distances, and higher lightness (or colour) contrast between test and context circles.

Usability of a theory of visual attention (TVA) for parameter-based measurement of attention II: evidence from two patients with frontal or parietal damage.

Based on a 'Theory of Visual Attention' (TVA), whole and partial report of brief letter arrays is presented as a diagnostic tool to estimate four clinically significant attentional components: perceptual processing speed, visual working memory storage capacity, efficiency of top-down control, and spatial distribution of attention. The procedure used was short enough to be applicable within a standard clinical setting. Two brain-damaged patients, selected based on lesion location and neuropsychological test profile, were compared to a control group of 22 healthy subjects.

Usability of a theory of visual attention (TVA) for parameter-based measurement of attention I: evidence from normal subjects.

The present study investigated the usability of whole and partial report of briefly displayed letter arrays as a diagnostic tool for the assessment of attentional functions. The tool is based on Bundesen's (1990, 1998, 2002; Bundesen et al., 2005) theory of visual attention (TVA), which assumes four separable attentional components: processing speed, working memory storage capacity, spatial distribution of attention, and top-down control.

Parameter-based assessment of spatial and non-spatial attentional deficits in Huntington's disease.

A major challenge for neuropsychological research on Huntington's disease is the identification of biomarkers for the disease at the level of cognitive functions. Given that cortical-striatal-thalamic circuits are particularly vulnerable, possible markers loading functionally on these brain regions should be particularly significant. We investigated whether parametric values derived from a 'theory of visual attention' (TVA) can serve that purpose.

Evidence of separable spatial representations in a virtual navigation task.

Three experiments investigated spatial orientation in a virtual navigation task. Subjects had to adjust a homing vector indicating their end position relative to the origin of the path. It was demonstrated that sparse visual flow was sufficient for accurate path integration.

Selective and interactive neural correlates of visual dimension changes and response changes.

In an event-related fMRI study, we investigated the neural correlates of visual dimension and response changes. We used a compound task, which required target selection by a singleton feature, a unique color or motion direction, before the appropriate motor response, which was determined by target orientation, could be selected. Both types of change elicited distinct patterns of activation, with dimension-change-related activation primarily in posterior visual areas and response-related activation primarily in motor-related areas of the parietal and frontal cortices.

The dynamics of operations in visual memory: a review and new evidence for oscillatory priming.

Evidence from neurophysiological studies indicates that the synchronization of distributed neuronal assemblies in the gamma frequency range is responsible for the integration of discrete stimulus components into coherent wholes (e.g., see Singer, 1999 for review).

Visual search for apparent-length targets is modulated by the Müller-Lyer illusion.

Is apparent object size represented in pre-attentive vision and can it influence visual search for size-defined targets in a spatially parallel manner? This question was investigated, using the Müller-Lyer illusion. Observers searched for a target line that was longer than the distractor lines. Test lines could be presented without context arrows (control); be adjoined by obtuse-angle context arrows (arrow heads pointing inward), making the lines appear longer; or by acute-angle arrows (heads pointing outward), making the lines appear shorter.

The Ebbinghaus illusion modulates visual search for size-defined targets: evidence for preattentive processing of apparent object size.

Five search experiments investigated whether the apparent size of objects is, like their retinal size, coded in preattentive vision. Observers searched for a target circle that was either larger or smaller than distractor circles, with both types of test circles surrounded by context circles modulating apparent size (i.e.