1,721,113 research outputs found
The contribution of working memory to divided attention.
No full textPrevious studies have indicated that increasing working memory (WM) load can affect the attentional selection of signals originating from one object/location. Here we assessed whether WM load affects also the selection of multiple objects/locations (divided attention). Participants monitored
either two object-categories (vs. one category; object-based divided attention) or two locations (vs. one location; space-based divided attention) while maintaining in WM either a variable number of objects (object-based WM load) or locations (space-based WM load). Behavioural results showed that WM load affected attentional performance irrespective of divided or focused attention. However, fMRI results showed that the activity associated with object-based divided attention increased linearly with increasing object-based WM load in the left and right intraparietal sulcus (IPS); while, in the same areas, activity associated with space-based divided attention was not affected by any type of WM load. These findings support the hypothesis that WM contributes to the maintenance of resource-demanding attentional sets in a domain-specific manner. Moreover, the dissociable impact of WM load on performance and brain activity suggests that increased IPS activation reflects a recruitment of additional,
domain-specific processing resources that enable dual-task performance under conditions of high WM load and high attentional demand
Contribution of low-level sensory features and object representation for short term memory of complex visual scenes
No full textPhysiological correlates of subjective time: Evidence for the temporal accumulator hypothesis
No full textClock-counter models, the most influential cognitive models of temporal computation, have been successful in explaining a large set of behavioral data. However, it remains unclear whether the component operations postulated in these models correspond to any specific biological mechanism. Using stimuli in different sensory modalities and manipulating physical properties known to bias the 'subjective' perception of time (speed for vision and pitch for audition), the present study aimed to highlight brain areas where activity correlates with the 'subjective' perception of time: a time accumulator according to clock-counter models. Using functional MRI we found that during the encoding of a temporal interval in the millisecond range (600 and 1000 ms), the hemodynamic response of a few brain regions correlated with the interval reproduction performance. For the visual modality, the activity of the putamen, the mid-insula and the mid-temporal cortex reflected the subjective interval duration, which was biased according to the different speeds of the visual stimuli. This effect was found only when subjects encoded the stimulus duration and was specific for the visual modality, where a significant overestimation of time with increasing speed was observed. These results demonstrate a definite relation between 'subjective time' and brain activity, supporting the hypothesis of a physiological correlate of time 'accumulation'
Auditory temporal expectations modulate activity in visual cortex
No full textTemporal expectation is the ability to make predictions and to use temporal information to anticipate the occurrence of future events. This capacity is associated with highly efficient perceptual and motor behaviors. However, how cognitive systems use temporal information to optimize behavior and what brain structures are engaged during these processes remains largely unknown. Neurophysiological and recent neuroimaging data have suggested that temporal expectations modulate activity not only in parietal and motor-related frontal regions, but also in occipital visual cortex, when the expected stimulus is a simple visual object. Here we investigate crossmodal properties and category selectivity of temporal expectations examining activity in visual cortex during expectation of auditory stimuli (the sound of hand-clapping or of a hammer-hammering). We found that activity in occipital cortex changed over time, reflecting the subject's temporal expectations about the upcoming auditory event. This modulatory effect included extrastriate visual areas known to process body-parts and tools, despite these were never presented visually during the experiment. However activity in these areas was not specific for the expected sound category, but it was rather related to the overall probability of the auditory target to occur. We conclude that crossmodal associations can influence activity in sensory-specific visual areas in an anticipatory manner, consistent with temporal expectations affecting activity in a distributed system of motor-related and sensory-related brain regions
FMRI correlates of visuo-spatial reorienting investigated with an attention shifting double-cue paradigm.
No full textThe control of visuo-spatial attention entails the joint contribution of goal-directed (endogenous) and stimulus-driven (exogenous) factors. However, little is known about the neural bases of the interplay between these two mechanisms. To address this issue, we presented endogenous (spatially informative) and exogenous (noninformative) visual cues sequentially within the same trial (double-cue paradigm) during fMRI, crossing factorially the validity of the two cues. We found that both endogenous and exogenous cues affected behavioral performance, speeding-up or slowing-down target discrimination when valid and invalid, respectively. Despite the double-cue paradigm maximizes the interplay between endogenous and exogenous factors, the two types of cue affected responses in an independent manner without any significant effect of congruence. The imaging data revealed increased activation in separate cortical areas following invalid endogenous and invalid exogenous cues. A fronto-parietal system was activated during invalid endogenous trials, whereas a region at the temporo-occipital junction was activated during invalid exogenous trials. Within both circuits, activity was unaffected by the validity of the other cue. These results indicate the existence of separate, noninteracting neural circuits for endogenous and exogenous reorienting of visuo-spatial attention
Multisensory objects and the orienting of spatial attention
No full textThe presentation of an auditory stimulus semantically-congruent with a visual element of a multi-objects display can enhance processing of that element. Here we used multisensory objects (MO) as non-informative cues in a spatial cueing paradigm, aiming to directly assess the interplay between MO integration and spatial attention. We presented two pictures (e.g., left — dog, right — cat) plus a central sound (e.g., a dog's bark) that defined the location of the MO (left, in this example). This was followed by a target (a Gabor patch) either at the MO location or in the opposite hemifield. Subjects discriminated the orientation of the Gabor, while ignoring all task-irrelevant pictures and sounds. Further, we manipulated the task requirements including `easy' or `difficult' discrimination (Gabor tilt = ±5° or ±10°), and by presenting either a single unilateral Gabor (Exp. 1, `low' competition) or two Gabors bilaterally (red and blue, with the target now defined by colour; Exp. 2, `high' competition). Functional imaging data revealed activation of frontal regions when the target was presented on the opposite side of the MO (invalid trials). The frontal eye-fields activated irrespective of task requirements, while the inferior frontal gyrus activated only when the MO-cue was invalid and competition was low (Exp. 1 only). These findings show that MOs automatically affect the distribution of spatial attention, and that re-orienting operations on invalid trials activate dorsal and ventral frontal areas depending on top-down task constraints. Overall, the results are consistent with the hypothesis linking the integration of multisensory objects with biases of spatial attention
Spatial orienting in complex audiovisual environments.
No full textPrevious studies on crossmodal spatial orienting typically used simple and stereotyped stimuli in the absence of any meaningful context. This study combined computational models, behavioural measures and functional magnetic resonance imaging to investigate audiovisual spatial interactions in naturalistic settings. We created short videos portraying everyday life situations that included a lateralised
visual event and a co-occurring sound, either on the same or on the opposite side of space. Subjects viewed the videos with or without eye-movements allowed (overt or covert orienting). For each video, visual and auditory saliency maps were used to index the strength of stimulus-driven signals,
and eye-movements were used as a measure of the efficacy of the audiovisual events for spatial orienting. Results showed that visual salience modulated activity in higher-order visual areas, whereas auditory salience modulated activity in the superior temporal cortex. Auditory salience modulated activity
also in the posterior parietal cortex, but only when audiovisual stimuli occurred on the same side of space (multisensory spatial congruence). Orienting efficacy affected activity in the visual cortex, within the same regions modulated by visual salience. These patterns of activation were comparable in overt and covert orienting conditions. Our results demonstrate that, during viewing of complex multisensory
stimuli, activity in sensory areas reflects both stimulus-driven signals and their efficacy for spatial orienting; and that the posterior parietal cortex combines spatial information about the visual and the auditory modality
Right Temporal-Parietal Junction engagement during spatial reorienting does not depend on strategic attention control.
No full textTargets presented outside the focus of attention trigger stimulus-driven spatial reorienting and activation of the right temporal-parietal junction (rTPJ). However, event-related functional resonance imaging (fMRI) studies that used task-irrelevant non-predictive cues systematically failed to activate rTPJ, suggesting that this region controls reorienting only when attention is shifted between two task-relevant locations. Here we challenge this view showing that non-predictive peripheral cues can affect activity in rTPJ, but only when they share a feature with the target: i.e. when they are set-relevant. Trials including a set-relevant cue plus a target on the uncued/unattended side produced the slowest reaction times and selective activation of the rTPJ. These findings demonstrate that rTPJ is not involved only in reorienting between two task-relevant locations, but engages also when non-predictive cues are set-relevant, thereby, irrespective of voluntary attention and breaches of task-related expectations
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