Browsing by Subject "Attentional load"
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Item Open Access Cortical processes underlying attentional modulations of dynamic vision(Bilkent University, 2022-09) Çatak, Esra NurVisual attention is one of the most fundamental cognitive functions guiding and influencing a various number of processes. However, how different neural mechanisms are modulated by selective attention to process information is still subject to debate. Utilizing electroencephalography (EEG), the current thesis focused on understanding the time course of visual information processing and its neural underpinnings with paradigms that operate in different attentional modes, such as visual masking, attentional load, and transparent motion design. First, we aimed to understand the role of spatial attention in information processing and its possible interactions with metacontrast masking mechanisms. The behavioral results revealed an interaction effect that suggests differential effects of spatial attention on metacontrast masking. The following EEG analyses revealed significant activation due to masking and attentional load on early negative components located over occipital and parieto-occipital scalp sites, followed by a late positive component centered over centro-parietal electrodes. These findings suggest that the effect of spatial attention may have distinct characteristics at different stages of sensory and perceptual processing regarding its relationship with metacontrast masking. Secondly, by employing a novel variant of transparent motion design with color and motion swapping, we aimed to isolate the object-based cueing effect from a possible feature-based explanation in both psychophysical measures and neural activities. Our results demonstrate that the behavioral effects of attentional cueing survived feature swaps, providing evidence for an object-based attention mechanism. We also observed event-related potential correlates of these object-based selection effects in the late N1 component range, over occipital and parieto-occipital scalp sites, significantly associated with the variation in behavioral performance. Our findings provide the first evidence of the role of the N1 component in object-based attention in this transparent-motion design under conditions that rule out possible feature-based explanations. Taken together, the present results highlight the substantial effects of selective attention on the processing of visual information after the initial entry of information into the visual system and before the completion of its processing.Item Open Access Neural processing of bottom-up perception of biological motion under attentional load(Elsevier, 2023-11-04) Nizamoğlu, Hilal; Ürgen, Burcu AyşenConsidering its importance for one’s survival and social significance, biological motion (BM) perception is assumed to occur automatically. Previous behavioral results showed that task-irrelevant BM in the periphery interfered with task performance at the fovea. Under selective attention, BM perception is supported by a network of regions including the occipito-temporal (OTC), parietal, and premotor cortices. Retinotopy studies that use BM stimulus showed distinct maps for its processing under and away from selective attention. Based on these findings, we investigated how bottom-up perception of BM would be processed in the human brain under attentional load when it was shown away from the focus of attention as a task-irrelevant stimulus. Participants (N = 31) underwent an fMRI study in which they performed an attentionally demanding visual detection task at the fovea while intact or scrambled point light displays of BM were shown at the periphery. Our results showed the main effect of attentional load in fronto-parietal regions and both univariate activity maps and multivariate pattern analysis results support the attentional load modulation on the task-irrelevant peripheral stimuli. However, this effect was not specific to intact BM stimuli and was generalized to motion stimuli as evidenced by the motion-sensitive OTC involvement during the presence of dynamic stimuli in the periphery. These results confirm and extend previous work by showing that task-irrelevant distractors can be processed by stimulus-specific regions when there are enough attentional resources available. We discussed the implications of these results for future studies.Item Open Access Neural underpinnings of biological motion perception under attentional load(Bilkent University, 2022-06) Çalışkan, Hilal NizamoğluHumans can detect and differentiate biological motion from non-biological motion stimuli effortlessly, even if the stimuli were shown as simplistic as a composition of moving dots (i.e. point-light displays [PLD]). Considering its survival and social significance, BM perception is assumed to occur automatically. Indeed, Thorn-ton and Vuong [1] showed that task-irrelevant BM in the periphery interfered with task performance at the fovea. However, the neural underpinnings of this bottom-up processing of BM lacks thorough examination in the field. Under selec-tive attention, BM perception is supported by a network of regions including the occipito-temporal, parietal, and premotor cortices. A retinotopy mapping study on BM showed distinct maps for its processing under and away from selective attention [2]. Based on these findings, we investigated how bottom-up percep-tion of BM would be processed under attentional load when it was shown away from the focus of attention as a task-irrelevant stimulus. Participants (N=31) underwent an fMRI study in which they performed an attentionally demand-ing visual detection task at the fovea while intact or scrambled PLDs of BM were shown at the periphery. Our results showed the main effect of attentional load in fronto-parietal regions; as well as, the main effect of peripheral stimuli in occipito-temporal cortex. Both univariate and multivariate pattern analysis results support the attentional load modulation on BM. Lastly, ROI results on each core node of BM processing network expanded these findings by showing that the attentional load modulation on both intact and scrambled BM stimuli were the strongest in bilateral occipito-temporal regions as compared to parietal and premotor cortices. In conclusion, BM was processed within the motion sensi-tive regions in the occipito-temporal cortex when shown away from the selective attention, and was modulated by attentional load.