Electronic Thesis and Dissertation Repository

Thesis Format



Master of Science




Mohsenzadeh, Yalda

2nd Supervisor

Joanisse, Marc F.


3rd Supervisor

Wang, Boyu



In our daily visual experience, our brain effortlessly categorizes countless objects, enabling us to perceive and interpret the world around us. This core object recognition process is vital for our survival and adaptive behavior, allowing us to recognize objects despite variations in appearance. The incredible speed at which we accomplish this task is a testament to the efficiency of our visual system and the significance of visual processing is evident in the allocation of nearly half of the neocortex in primates to this function. Unraveling the intricacies of how the human visual system tackles this complex challenge has long been a goal in visual neuroscience. Researchers have explored the mechanisms underlying object recognition and the role of the neocortex, employing various studies and experiments. But how does our brain recognize objects in challenging visual conditions? In our study, we conducted a visual experiment to examine participants' ability to recognize a target amidst a rapid series of images, creating a challenging visibility condition. Our findings revealed a noteworthy distinction in the processing of seen (visible) and unseen (invisible) stimuli. Specifically, we observed a significant divergence in processing occurring later in the timeline, ~170 milliseconds after the target onset, while no significant differences were detected during the initial stages of processing. These results suggest that early processing stages exhibit similar characteristics for both visible and invisible stimuli, indicative of feedforward processing. Feedforward processing involves the transmission of information from lower to higher levels within the visual hierarchy. However, our findings highlight the importance of late recurrent processes, which involve the transmission of information within the same area or from higher to lower levels of the visual hierarchy. The substantial disparity observed in the later stages of processing indicates that these recurrent processes play a crucial role in visibility under challenging conditions.

Summary for Lay Audience

Our brain is incredibly skilled at recognizing objects, allowing us to understand and navigate the world around us. This ability is crucial for our survival and depends on the efficient processing of visual information in our brain. Scientists have been long studying how our brain recognizes objects and the role of different brain regions in this process. In this study, we conducted an experiment to investigate how our brain recognizes objects under challenging conditions. We found that there is a significant difference in how our brain processes seen and unseen stimuli. While early processing stages are similar for both types of stimuli, later stages show a clear distinction. This suggests that the brain processes, which happen late in the brain after the initial processes, are crucial for recognizing objects under difficult conditions. These findings shed light on the complex mechanisms of object recognition in the human brain.