Browsing by Subject "MVPA"

Now showing 1 - 4 of 4

Open Access
Behavioral and neural investigation on the effects of prior information on biological motion perception
(2023-07) Elmas, Hüseyin Orkun
The capacity to understand the actions of others, a cognitive phenomenon known as biological motion perception, is crucial for humans. Recent research demonstrates that biological motion is processed distinctively compared to the motions of inanimate objects. A dedicated brain network for processing biological motion and actions has been uncovered through fMRI studies. M/EEG studies have revealed time windows within which biological motion processing occurs. Despite these findings, a comprehensive understanding of the fundamental mechanisms driving biological motion perception, especially the effects of top-down processes, and the temporal dimension of these effects still remain unexplored. Recent evidence in visual perception suggests that prior knowledge and expectations affect visual perception; however, the generalizability of these effects to socially important stimuli, such as biological motion, is still unknown. This study aims to illuminate the effects of prior information on the behavioral and neural mechanisms of biological motion perception. To this end, we conducted a series of behavioral experiments and an EEG experiment to investigate the effects of prior information on biological motion perception. Through our behavioral experiments, we found that prior information influences the individuation process of biological motion, albeit conditionally. Specifically, this influence is observed only when the cue carries information about the type of action in the biological motion stimuli, and the reliability of the cue is high, at 75%. Our EEG experiment demonstrated that correct and incorrect prior information affects the temporal dimension of biological motion perception, suggesting an early effect of prior information during biological motion processing. More-over, a comparison of the temporal generalization matrices suggested that correct prior information accelerates biological motion perception by accelerating the for-mation of related representations in the brain relative to the neutral condition. Additionally, the temporal generalization analysis results illustrate a sequence in representations within brain activity: the representation of location information precedes the representation of action type of biological motion. These results suggest that computational models, developed to model the underlying mechanisms of biological motion perception, should consider the implications of predictive processes and their temporal dimension. Furthermore, these findings support the applicability of predictive models to not only low-level stimuli but also to higher-level stimuli.
Open Access
Neural underpinnings of biological motion perception under attentional load
(2022-06) Çalışkan, Hilal Nizamoğlu
Humans 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.
Open Access
Perception of built environments and its neural modulation by the behavioral goals of the perceiver
(2023-07) Koç, Aysu Nur
A scene is a view of an environment with a spatial layout one can act within. Scene perception has been studied extensively in the neuroscience literature, examining changes in neural activity across the brain and scene-selective regions (PPA, RSC, OPA), in response to various low and high-level features and tasks. The focus of the field has been mostly on outdoor scenes based on broad categorical differences (e.g. natural/man-made) or basic differences between otherwise similar indoor environments (e.g. ceiling height) and behavioral components regarding scene perception have been overlooked. Interactions with fields such as environ-mental psychology or neuroarchitecture, which could inspire a more ecologically valid study of scenes, are rare. Hereby, we investigated the perception of built environments where we spend most of our time, drew our categorization method from the architecture literature, and employed multiple tasks. The categories were elements that (i) allow our access to and circulation within environments (entrances, exits, corridors, stairs); and that (ii) do not directly aid locomotion but rather serve human needs (restrooms, eating and seating areas). FMRI scans were obtained from 23 participants as they viewed scenes from built environments and performed two tasks: a categorization task based on the main afforded action differences between the defined categories, and an approach-avoidance task where participants decided to enter the scene or not, measuring the initial action regarding an environment. Scene-selective ROIs were defined with a localizer session. Univariate analyses did not reveal strong differences between the tasks. Searchlight MVPA revealed categories, but not tasks, are classified at the whole-brain level, at the lingual and parahippocampal gyri, the SMA, and the occipital cortex. Model-based RSA at the ROI level revealed that tasks modulate activation patterns to built environments in all three ROIs, but do not entirely explain them, whereas categorical and visual models did not correlate with the activation patterns in any of these regions. We utilize an interdisciplinary perspective to scene perception to expand the ecological validity of the stimuli and task con-tent, showing that neural responses to built environments are modulated by the behavioral goals of the observer at the ROI level, and stimulus category at the whole-brain level.
Open Access
Task-modulated neural responses in scene-selective regions of the human brain
(Elsevier Ltd, 2025-02) Koç, Aysu Nur; Ürgen, Burcu Ayşen; Afacan, Yasemin
The study of scene perception is crucial to the understanding of how one interprets and interacts with their environment, and how the environment impacts various cognitive functions. The literature so far has mainly focused on the impact of low-level and categorical properties of scenes and how they are represented in the scene-selective regions in the brain, PPA, RSC, and OPA. However, higher-level scene perception and the impact of behavioral goals is a developing research area. Moreover, the selection of the stimuli has not been systematic and mainly focused on outdoor environments. In this fMRI experiment, we adopted multiple behavioral tasks, selected real-life indoor stimuli with a systematic categorization approach, and used various multivariate analysis techniques to explain the neural modulation of scene perception in the scene-selective regions of the human brain. Participants (N = 21) performed categorization and approach-avoidance tasks during fMRI scans while they were viewing scenes from built environment categories based on different affordances ((i)access and (ii)circulation elements, (iii)restrooms and (iv)eating/seating areas). ROI-based classification analysis revealed that the OPA was significantly successful in decoding scene category regardless of the task, and that the task condition affected category decoding performances of all the scene-selective regions. Model-based representational similarity analysis (RSA) revealed that the activity patterns in scene-selective regions are best explained by task. These results contribute to the literature by extending the task and stimulus content of scene perception research, and uncovering the impact of behavioral goals on the scene-selective regions of the brain.