Here today, gone tomorrow - adaptation to change in memory-guided visual search

Visual search for a target object can be facilitated by the repeated presentation of an invariant configuration of nontargets ('contextual cueing'). Here, we tested adaptation of learned contextual associations after a sudden, but permanent, relocation of the target. After an initial learning phase targets were relocated within their invariant contexts and repeatedly presented at new locations, before they returned to the initial locations. Contextual cueing for relocated targets was neither observed after numerous presentations nor after insertion of an overnight break. Further experiments investigated whether learning of additional, previously unseen context-target configurations is comparable to adaptation of existing contextual associations to change. In contrast to the lack of adaptation to changed target locations, contextual cueing developed for additional invariant configurations under identical training conditions. Moreover, across all experiments, presenting relocated targets or additional contexts did not interfere with contextual cueing of initially learned invariant configurations. Overall, the adaptation of contextual memory to changed target locations was severely constrained and unsuccessful in comparison to learning of an additional set of contexts, which suggests that contextual cueing facilitates search for only one repeated target location

The role of unique color changes and singletons in attention capture

Previous studies have shown that a sudden color change is typically less salient in capturing attention than the onset of a new object. Von Mühlenen, Rempel, and Enns (Psychological Science 16: 979-986, 2005) showed that a color change can capture attention as effectively as the onset of a new object given that it occurs during a period of temporal calm, where no other display changes happen. The current study presents a series of experiments that further investigate the conditions under which a change in color captures attention, by disentangling the change signal from the onset of a singleton. The results show that the item changing color receives attentional priority irrespective of whether this change goes along with the appearance of a singleton or not

Figural Completion in Visual Search

Die Integration von Teilfragmenten zu einem kohärenten und zusammenhängenden Objekt stellt einen wesentlichen Aspekt der visuellen Informationsverarbeitung dar. In der vorliegenden, kumulativen Dissertation wird diese Frage der Objektintegration untersucht indem Figurbildungsmechanismen und deren Rolle für die visuelle Suche analysiert werden. In einer Reihe von Experimenten mit virtuellen Figurkonfigurationen (‚Kanizsa’ Figuren) konnte gezeigt werden, dass die Sucheffizienz von der integrierten Formrepräsentation einzelner Objektfragmente abhängt. Die Steuerung von Suchprozessen lässt sich demnach auf Basis eines Extraktionsmechanismus verstehen, der vorhandene visuelle Informationen zu salienten Regionen gruppiert bzw. segmentiert und auf formsensitive Verarbeitungsprozesse in okzipito-parietalen Arealen zurückgreift. Komplementär zu diesen Mechanismen der figuralen Segmentation konnte zudem in einer weiteren Experimentalserie gezeigt werden, dass auch aufgabenrelevante Charakteristika auf gruppierungsspezifische Suchprozesse einwirken können. Somit sind Figurbildungsprozesse in der visuellen Suche sowohl durch die Berechnung einer salienten Region als auch durch entsprechende Anforderungen der Aufgabe modifizierbar und erklärbar

The effect of task-irrelevant objects in spatial contextual cueing

During visual search, the spatial configuration of the stimuli can be learned when the same displays are presented repeatedly, thereby guiding attention more efficiently to the target location (contextual cueing effect). This study investigated how the presence of a task-irrelevant object influences the contextual cueing effect. Experiment 1 used a standard T/L search task with “old” display configurations presented repeatedly among “new” displays. A green-filled square appeared at unoccupied locations within the search display. The results showed that the typical contextual cueing effect was strongly reduced when a square was added to the display. In Experiment 2, the contextual cueing effect was reinstated by simply including trials where the square could appear at an occupied location (i.e., underneath the search stimuli). Experiment 3 replicated the previous experiment, showing that the restored contextual cueing effect did not depend on whether the square was actually overlapping with a stimulus or not. The final two experiments introduced a display change in the last epoch. The results showed that the square does not only hinder the acquisition of contextual information but also its manifestation. These findings are discussed in terms of an account where effective contextual learning depends on whether the square is perceived as part of the search display or as part of the display background

Local item density modulates adaptation of learned contextual cues

In everyday scenes, searched-for targets do not appear in isolation, but are embedded within configurations of non-target or distractor items. If the position of the target relative to the distractors is invariant, such spatial contingencies are implicitly learned and come to guide visual scanning ("contextual cueing"). However, the effectiveness of contextual cueing depends heavily on the consistency between bottom-up perceptual input and context memory: following configural learning, re-locating targets to an unexpected location within an unchanged distractor context completely abolishes contextual cueing, and gains deriving from the invariant context recover only very slowly with increasing exposure to the changed displays. The current study induces variations of the local target context, i.e., item density, to investigate the relation between this factor and contextual adaptation. The results showed that learned contextual cues can be adapted quickly if the target is re-positioned to a sparse ..

Amodal Completion of a Target Template Enhances Attentional Guidance in Visual Search

When searching for a target object in cluttered environments, our visual system appears to complete missing parts of occluded objectsa mechanism known as amodal completion. This study investigated how different variants of completion influence visual search for an occluded target object. In two experiments, participants searched for a target among distractors in displays that either presented composite objects (notched shapes abutting an occluding square) or corresponding simple objects. The results showed enhanced search performance when composite objects were interpreted in terms of a globally completed whole. This search benefit for global completions was found to be dependent on the availability of a coherent, informative simple-object context. Overall, these findings suggest that attentional guidance in visual search may be based on a target template that represents a globally completed image of the occluded (target) object in accordance with prior experience

Object maintenance beyond their visible parts in working memory

Completion of a partially occluded object requires that a representation of the whole is constructed based on the information provided by the physically specified parts of the stimulus. Such processes of amodal completion rely on the generation and maintenance of a mental image that renders the completed object in visual working memory (VWM). The present study examined this relationship between VWM storage and processes of object completion. We recorded event-related potentials to track VWM maintenance by means of the contralateral delay activity (CDA) during a change detection task in which composite objects (notched shapes abutting an occluding shape) to be memorized were primed to induce either a globally completed object or a noncompleted, mosaic representation. The results revealed an effect of completion in VWM despite physically identical visual input: change detection was more accurate for completed compared with mosaic representations when observers were required to memorize two objects, and these differences were reduced with four memorized items. At the electrophysiological level, globally completed (vs. mosaic) objects gave rise to a corresponding increase in CDA amplitudes. These results indicate that although incorporating the occluded portions of the presented shapes requires mnemonic resources, the complete object representations thus formed in VWM improve change detection performance by providing a more simple, regular shape. Overall, these findings demonstrate that mechanisms of object completion modulate VWM, with the memory load being determined by the structured representations of the memorized stimuli

Object integration requires attention: visual search for Kanizsa figures in parietal extinction

The contribution of selective attention to object integration is a topic of debate: integration of parts into coherent wholes, such as in Kanizsa figures, is thought to arise either from pre-attentive, automatic coding processes or from higher-order processes involving selective attention. Previous studies have attempted to examine the role of selective attention in object integration either by employing visual search paradigms or by studying patients with unilateral deficits in selective attention. Here, we combined these two approaches to investigate object integration in visual search in a group of five patients with left-sided parietal extinction. Our search paradigm was designed to assess the effect of left- and right-grouped nontargets on detecting a Kanizsa target square. The results revealed comparable reaction time (RT) performance in patients and controls when they were presented with displays consisting of a single to-be-grouped item that had to be classified as target vs. nontarget. However, when display size increased to two items, patients showed an extinction-specific pattern of enhanced RT costs for nontargets that induced a partial shape grouping on the right, i.e., in the attended hemifield (relative to the ungrouped baseline). Together, these findings demonstrate a competitive advantage for right-grouped objects, which in turn indicates that in parietal extinction, attentional competition between objects particularly limits integration processes in the contralesional, i.e., left hemifield. These findings imply a crucial contribution of selective attentional resources to visual object integration

Taking attention out of context: Frontopolar Transcranial Magnetic Stimulation abolishes the formation of new context memories in visual search

This study investigates the causal contribution of the left frontopolar cortex (FPC) to the processing of violated expectations from learned target-distractor spatial contingencies during visual search. The experiment consisted of two phases: learning and test. Participants searched for targets presented either among repeated or nonrepeated target-distractor configurations. Prior research showed that repeated encounters of identically arranged displays lead to memory about these arrays, which then can come to guide search (contextual cueing effect). The crucial manipulation was a change of the target location, in a nevertheless constant distractor layout, at the transition from learning to test. In addition to this change, we applied repetitive transcranial magnetic stimulation (rTMS) over the left lateral FPC, over a posterior control site, or no rTMS at all (baseline; between-group manipulation) to see how FPC rTMS influences the ability of observers to adapt context-based memories acquired in the training phase. The learning phase showed expedited search in repeated relative to nonrepeated displays, with this context-based facilitation being comparable across all experimental groups. For the test phase, the recovery of cueing was critically dependent on the stimulation site: Although there was evidence of context adaptation toward the end of the experiment in the occipital and no-rTMS conditions, observers with FPC rTMS showed no evidence of relearning at all after target location changes. This finding shows that FPC plays an important role in the regulation of prediction errors in statistical context learning, thus contributing to an update of the spatial target-distractor contingencies after target position changes in learned spatial arrays