سميرا گوهري

In visual working memory, the ability to accurately maintain relationships between object features is of special importance, as in the observation of multi-object scenes, a “binding error” may occur. For example, the simultaneous perception of a red square an‎d a green circle may be interpreted as a green square an‎d a red circle. This study investigated the mentioned model in fragile visual memory through EEG signals. The main idea of the research is to separate feature bindings based on spatial location an‎d independent of it. For this purpose, three features—color, location, an‎d orientation—were selec‎ted. By defining six positions in the visual field, a model with 216 independent parameters was proposed. In 1980, Anne Treisman first introduced the Feature Integration Theory (FIT). This theory suggests that for each possible feature, there are mental maps in the visual cortex known as “feature maps.” Although this model has been discussed in behavioral studies on perception, it has not yet been fully developed in working memory. Hence, the primary aim of this project is to examine the model within the domain of fragile short-term memory using electroencephalogram (EEG) signals. Modeling of EEG signals revealed that after rapid presentation of two-dimensional stimuli composed of combinations of color, location, an‎d orientation features, the pattern of neural activity in occipito-parietal regions clearly reflects the bound structure of these features. This spatial differentiation in feature-integration representation indicates specific involvement of visual–spatial areas of the brain in fragile memory representation. Within the time window of 200–600 ms after stimulus onset, a significant increase in theta-ban‎d power (4–8 Hz) was observed in frontal-central regions. This pattern aligns with the known role of the theta ban‎d in information maintenance within active memory an‎d can be interpreted as a marker of the retention process in fragile memory. Interestingly, in the four-shape condition, theta-ban‎d power increased within 0–200 ms, which may be attributed to faster an‎d more efficient encoding of information under lower cognitive load. Across all experimental conditions, a reduction in alpha-ban‎d power (8–12 Hz) in occipital regions was reported between 200 an‎d 600 ms. This reduction, often associated with increased visual processing an‎d decreased cortical inhibition, indicates active involvement of visual networks in stimulus feature processing an‎d maintenance. However, in the six-shape condition, this reduction was not only more pronounced but also more sustained, suggesting higher visual processing deman‎ds under greater memory load. In the final stage of each trial (600–1000 ms), an increase in beta ban‎d power (13–30 Hz) in frontal an‎d central regions was observed. This activity is linked to executive functions such as cognitive control, response selec‎tion, an‎d motor preparation. Notably, the spatial pattern differed between conditions: in the six-shape test, beta-ban‎d activation was more focused in prefrontal areas, whereas in the four-shape test, it was more diffuse an‎d widespread. This difference may indicate regulatory an‎d integrative mechanisms for motor response under varying stimulus complexity. Overall, the findings suggest that neural networks involved in processing an‎d maintaining feature bindings in fragile memory are organized in a stepwise manner with distinct neural rhythms: theta representing memory retention, alpha relating to visual processing, an‎d beta associated with response preparation an‎d executive functioning.

حافظه فرجايل , سيگنال‌هاي EEG

fragile memory , EEG signals

Samira Gohari

Dr. Borhan Beigzadeh