Browsing by Subject "Expectation"

Now showing 1 - 6 of 6

Open Access
Behavioral and computational investigation of the effect of prior knowledge on visual perception
(2021-01) Ürgen, Buse Merve
Visual perception results from the dynamic interaction of bottom-up and topdown processes. Top-down prior knowledge and expectations can guide us to predict upcoming events and even determine what we see in an ambiguous or noisy sensory stimulus. Despite the well-established facilitating effects of expectations on recognition or decision-making, whether and how early sensory processes are affected by expectations remain unclear. This dissertation attempts to investigate the effect of expectations on early visual processes. To this end, we used behavioral experiments to examine the effects of expectation on visual perception at the threshold level and implemented a recursive Bayesian model and a recurrent cortical model to unravel the computational mechanisms underlying those effects. In the behavioral experiments, we systematically manipulated expectation’s validity in separate sessions and measured duration thresholds, which is the shortest presentation time sufficient to achieve a certain success level. Our behavioral findings showed that valid expectations do not reduce the thresholds, rather unmet expectations lead them to increase. Next, using a recursive Bayesian updating scheme, we modeled the empirical data obtained in the behavioral experiments. Model fitting showed that higher thresholds observed in the unmet expectations are not due to a change in the internal parameters of the system. Instead, additional computations are required by the system to complete the sensory process. Finally, within the predictive processing framework, we implemented a recurrent cortical model to explain the behavioral findings and discuss possible neural mechanisms underlying the observed effects. The cortical model findings were in agreement with the Bayesian model results, revealing that longer processing is needed when expectations are not met. Overall, the computational models that are proposed in this study provide a parsimonious explanation for the observed behavioral effects. The proposed experimental paradigm and the computational models offer a novel framework that can be extended and used in other stimuli, tasks, and sensory modalities.
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
The effect of orientation-related prior probability information on contrast perception
(2019-07) Nazlı, İlayda
It is known that visual perception is the product of sensory input and prior probability information. Previous studies support well that expectation influence recognition and decision-making; however, we have limited knowledge about how expectation influences low level visual processing. In the current study, we examine the effect of expectation on early visual processing. That is, we provide task-irrelevant expectation cue related to the orientation of target Gabor grating, and we ask participants to indicate the spatial location of target grating while systematically manipulating its contrast level. In addition, we examine how different expectation validities (i.e. 75%, 50%, 100%) and neutral expectation cue affect visual perception. In Experiment 1, where the orientation of expectation cue and target gratings are vertical or horizontal, contrast threshold is lower in congruent trials at 75% validity condition. In Experiment 2, where the orientation of cue grating implies specific range (i.e. ±15 around 0 or 90), contrast threshold is lower in congruent trials at 75% and 50% validity condition. In Experiment 3B, where the orientation of expectation cue and target Gabor grating are within wider range (i.e. ±30 around 0 or 90), contrast threshold is lower in congruent trials at 75% validity condition. In Experiment 3A, where the orientation of expectation cue and target Gabor grating are within a specific range (i.e. ±15 around 0 or 90) contrast threshold is lower in congruent trials at 75% and 50% validity condition. In Experiment 3B, where the orientation of expectation cue and target Gabor grating are within wider range (i.e. ±30 around 0 or 90), contrast threshold is lower in congruent trials at 75% validity condition.
Open Access
Predictive processing in the cortical network of biological motion perception
(2024-07) Tunca, Murat Batu
The literature on biological motion processing argues that it occurs in occipitotemporal, parietal and frontal regions of the brain. Nevertheless, the literature is currently unable to explain how this processing is affected by expectations. Although models exist to explain how biological motion is perceived, they usually ignore top-down processes. To this end, the current fMRI study presented two point-light displays (embedded in noise) on either side of the screen to the participants (N=29). One of the displays was a biological motion (walking or kicking) whereas the other one was its scrambled version. The participants were asked to report the location of the biological motion. Importantly, before the presentation of motions, the participants were shown a cue about the action type (walking or kicking) which was congruent with the motion 75% of the time. There were also two additional conditions in which the cue was uninformative about the action (neutral condition) or there were no motion stimuli at all. As expected, the action observation network (consisting of pSTS, parietal cortex and IFG) showed a clear and strong activation during the conditions that a motion was present. However, these regions have failed to significantly discriminate between congruent and incongruent conditions. It should be acknowledged that this lack of significant result might be caused by the low number of trials. In order to better investigate the connections within action observation network, a DCM analysis was conducted. The winning DCM model has successfully shown the presence of feedback connections in the biological motion processing. More specifically, the model argues that both feedforward and feedback modulatory connections are present during congruent, incongruent and neutral conditions. In sum, the study highlights the importance of incorporating top-down signals such as expectations in the computational models of biological motion perception.
Open Access
Unmet expectations about material properties delay perceptual decisions
(Elsevier, 2023-05-21) Malik, Amna; Doerschner, Katja; Boyacı, Hüseyin
Based on our expectations about material properties, we can implicitly predict an object’s future states, e.g., a wine glass falling down will break when it hits the ground. How these expectations affect relatively low-level perceptual decisions, however, has not been systematically studied previously. To seek an answer to this question, we conducted a behavioral experiment using animations of various familiar objects (e.g., key, wine glass, etc.) freely falling and hitting the ground. During a training session, participants first built expectations about the dynamic properties of those objects. Half of the participants (N = 28) built expectations consistent with their daily lives (e.g., a key bounces rigidly), whereas the other half learned an atypical behavior (e.g., a key wobbles). This was followed by experimental sessions, in which expectations were unmet in 20% of the trials. In both training and experimental sessions, the participant’s task was to report whether the objects broke or not upon hitting the ground. Critically, a specific object always remained intact or broke - only the manner in which it did so differed. For example, a key could wobble or remain rigid but never break. We found that participants’ reaction times were longer when expectations were unmet, not only for typical material behavior but also when those expectations were atypical and learned during the training session. Furthermore, we found an interplay between long-term and newly learned expectations. Overall, our results show that expectations about material properties can impact relatively low-level perceptual decision-making processes.
Open Access
Unmet expectations delay sensory processes
(Elsevier, 2021-01-02) Ürgen, Buse Merve; Boyacı, Hüseyin
Expectations strongly affect and shape our perceptual decision-making processes. Specifically, valid expectations speed up perceptual decisions, and determine what we see in a noisy stimulus. Despite the well-established effects of expectations on decision-making, whether and how they affect low-level sensory processes remain elusive. To address this problem, we investigated the effect of expectation on temporal thresholds in an individuation task (detection of the position of an intact image, a house or face). We found that compared to a neutral baseline, thresholds increase when the intact images are of the unexpected category, but remain unchanged when they are of the expected category. Using a recursive Bayesian model with dynamic priors we show that delay in sensory processes is the result of further processing, consequently longer time, required in case of violated expectations. Expectations, however, do not alter internal parameters of the system. These results reveal that sensory processes are delayed when expectations are not met, and a simple parsimonious computational model can successfully explain this effect.