Browsing by Subject "Motion perception"

Now showing 1 - 9 of 9

Open Access
Audiovisual associations alter the perception of low-level visual motion
(Frontiers Research Foundation, 2015) Kafaligonul H.; Oluk, C.
Motion perception is a pervasive nature of vision and is affected by both immediate pattern of sensory inputs and prior experiences acquired through associations. Recently, several studies reported that an association can be established quickly between directions of visual motion and static sounds of distinct frequencies. After the association is formed, sounds are able to change the perceived direction of visual motion. To determine whether such rapidly acquired audiovisual associations and their subsequent influences on visual motion perception are dependent on the involvement of higherorder attentive tracking mechanisms, we designed psychophysical experiments using regular and reverse-phi random dot motions isolating low-level pre-attentive motion processing. Our results show that an association between the directions of low-level visual motion and static sounds can be formed and this audiovisual association alters the subsequent perception of low-level visual motion. These findings support the view that audiovisual associations are not restricted to high-level attention based motion system and early-level visual motion processing has some potential role. © 2015 Kafaligonul and Oluk.
Open Access
Behavioral and neural investigation on the effect of spatial attention on surround suppression
(2023-09) Kınıklıoğlu, Merve
When a visual stimulus is presented together with other stimuli surrounding it, behavioral sensitivity and neural responses may change, often reduce, compared to when the same stimulus is presented alone. This is commonly referred to as center-surround interaction or surround suppression, and it is one of the most fundamental mechanisms in biological vision. It is well documented that in motion perception, center-surround interaction is affected by the size and contrast of the stimulus. As the size of a drifting grating increases, motion direction discrimination performance, as well as neural activity in one of the main cortical motion processing areas, medial temporal complex (MT+), decreases if the grating has high contrast (surround suppression). Whereas, when the size increases within certain limits, both the discrimination performance and the neural activity in MT+ may increase if the grating has low contrast (surround facilitation). On the other hand, spatial attention is known to modulate surround suppression both in humans and non-human animals with static stimuli. No previous study, how-ever, has directly and systematically investigated the effect of the spatial extent of attention on surround suppression in human motion perception. The studies presented in this dissertation aim to investigate the effect of the extent of spatial attention on center-surround interaction in visual motion processing. In our experiments, we used two attention conditions and a novel stimulus design, where a ‘center’ and a ‘surround’ drifting grating were presented to the participants. Under one of the attention conditions, which we call the ‘narrow-attention’ condition, participants performed a task that limited their attention to the central part of the stimulus. Under the other attention condition, which we call the ‘wide-attention’ condition, participants performed tasks that required them to extend their attention to both the center and surround gratings. Using this experimental paradigm, we measured motion direction discrimination thresholds behaviorally and cortical activity with fMRI. Behaviorally, we found increased thresholds, that is, stronger surround suppression, under the wide attention condition. In the hu-man homolog of MT+ (hMT+), we found that increasing the spatial extent of attention leads to reduced cortical responses, that is, to stronger neural suppression. This was not the case for the activity in the primary visual cortex (V1). Finally, we show that a parsimonious computational model that incorporates spatial attention and response normalization can successfully predict the response patterns in hMT+ and V1. Furthermore, the model could provide a link between cortical responses and behavioral thresholds. Overall, our findings and analyses showed that the behavioral effect can be successfully predicted by hMT+ activity. These results reveal the critical role of spatial attention on surround suppression, namely that surround suppression in motion perception becomes stronger with a wider attention field, and reveal possible cortical mechanisms underpinning the effect.
Open Access
Characterizing surround suppression in motion direction perception
(2021-06) Kurt, Aslı Gül
Visual perception is often achieved by surround modulation mechanisms, which help us pool individual information in our visual ﬁeld. This mechanism is also prominent in motion perception, namely motion discrimination. A center-surround antagonistic organization aids motion perception using these modula-tion mechanisms, which are facilitation or suppression. Decisions to which modu-lation type will take place are usually manipulated by changing size and contrast of drifting Gabor disc stimuli. Because a systematic investigation of these mech-anisms is not conducted in prior research, we have used three diﬀerent types of stimulus (small disc, annular, and large disc grating) to see whether there is a fa-cilitative or suppressive pattern between duration thresholds of these stimuli. To achieve this, we performed a behavioral study, that would assess motion discrim-ination thresholds of human participants for these stimuli via adaptive staircase procedures. Then, we looked for three possible pooling regimes by comparing duration thresholds of small disc-annular-large disc grating stimulus sets: eﬃ-cient or ineﬃcient (weak or strong suppression) pooling. We found that duration thresholds of large disc gratings were almost greater than small disc or annular gratings almost all the time in both contrast levels, which indicated a strong sup-pression. We have also conducted simulations of divisive normalization models and observed that modulation mechanisms were more prominent in simulated duration thresholds using MT parameters from literature than V1. Although previous literature suggests that MT region produces facilitative or suppressive eﬀects within itself, we are not able to postulate a speciﬁc brain region creating strong suppressive pooling we observed in our behavioral data. This is why this study is a critical next step for future neuroimaging studies.
Open Access
Comparing the performance of humans and 3D-convolutional neural networks in material perception using dynamic cues
(2019-07) Mehrzadfar, Hossein
There are numerous studies on material perception in humans. Similarly, there are various deep neural network models that are trained to perform different visual tasks such as object recognition. However, the intersection of material perception in humans and deep neural network models has not been investigated to our knowledge. Especially, the importance of the ability of deep neural networks in categorizing materials and also comparing human performance with the performance of deep convolutional neural networks has not been appreciated enough. Here we have built, trained and tested a 3D-convolutional neural network model that is able to categorize the animations of simulated materials. We have compared the performance of the deep neural network with that of humans and concluded that the conventional training of deep neural networks is not necessarily giving the optimal state of the network to be compared to the performance of the humans. In the material categorization task, the similarity between the performance of humans and deep neural networks increases and reaches the maximum similarity and then decreases as we train the network further. Also, by training the 3D-CNN on regular, temporally consistent animations and also training it on the temporally inconsistent animations and comparing the results we found out that the 3D-CNN model can use spatial information in order to categorize the material animations. In other words, we found out that the temporal, and consistent motion information is not necessary for the deep neural networks in order to categorize the material animations.
Open Access
Contrast affects fMRI activity in middle temporal cortex related to center-surround interaction in motion perception
(Frontiers Research Foundation, 2016) Türkozer, Halide B.; Pamir, Zahide; Boyacı, Hüseyin
As the size of a high contrast drifting Gabor patch increases, perceiving its direction of motion becomes harder. However, the same behavioral effect is not observed for a low contrast Gabor patch. Neuronal mechanisms underlying this size-contrast interaction are not well understood. Here using psychophysical methods and functional magnetic resonance imaging (fMRI), we investigated the neural correlates of this behavioral effect. In the behavioral experiments, motion direction discrimination thresholds were assessed for drifting Gabor patches with different sizes and contrasts. Thresholds increased significantly as the size of the stimulus increased for high contrast (65%) but did not change for low contrast (2%) stimuli. In the fMRI experiment, cortical activity was recorded while observers viewed drifting Gabor patches with different contrasts and sizes. We found that the activity in middle temporal (MT) area increased with size at low contrast, but did not change at high contrast. Taken together, our results show that MT activity reflects the size-contrast interaction in motion perception. © 2016 Turkozer, Pamir and Boyaci.
Open Access
Distinct patterns of surround modulation in V1 and hMT+
(Academic Press Inc., 2020) Er, Görkem; Pamir, Zahide; Boyacı, Hüseyin
Modulation of a neuron’s responses by the stimuli presented outside of its classical receptive field is ubiquitous in the visual system. This “surround modulation” mechanism is believed to be critical for efficient processing and leads to many well-known perceptual effects. The details of surround modulation, however, are still not fully understood. One of the open questions is related to the differences in surround modulation mechanisms in different cortical areas, and their interactions. Here we study patterns of surround modulation in primary visual cortex (V1) and middle temporal complex (hMT+) utilizing a well-studied effect in motion perception, where human observers’ ability to discriminate the drift direction of a grating improves as its size gets bigger if the grating has a low contrast, and deteriorates if it has a high contrast. We first replicated the findings in the literature with a behavioral experiment using small and large (1.67 and 8.05 degrees of visual angle) drifting gratings with either low (2%) or high (99%) contrast presented at the periphery. Next, using functional MRI, we found that in V1 with increasing size cortical responses increased at both contrast levels. Whereas in hMT+ with increasing size cortical responses remained unchanged or decreased at high contrast, and increased at low contrast, reflecting the perceptual effect. We also show that the divisive normalization model successfully predicts these activity patterns, and establishes a link between the behavioral results and hMT+ activity. We conclude that surround modulation patterns in V1 and hMT+ are different, and that the size-contrast interaction in motion perception is likely to originate in hMT+.
Open Access
Examining the effects of audiovisual associations on motion perception through task-based fMRI
(Yerkure Tanitim ve Yayincilik Hizmetleri A.S., 2018) Kafalıgönül, Hulusi
Examining the effects of audiovisual associations on motion perception through task-based fMRI Objective: Previous studies showed that associative learning can lead to drastic changes in perceptual experience and unexpected levels of sensory plasticity in the adult brain. However, how associative learning is involved in shaping perception and the underlying neural mechanisms are quite poorly understood. In the current study, by taking advantage of well-studied visual motion-processing hierarchy, the roles of different brain areas in audiovisual association-induced changes in motion perception are investigated. Method: Using a previously developed audiovisual associative paradigm, behavioral and Blood Oxygen Level Dependent (BOLD) data were collected from adult human participants (n=13) before and after the association phase. Behavioral data were collected through reports on visual motion direction. Functional magnetic resonance imaging (fMRI) was based on block design and the functional data were analyzed according to a general linear model. Results: Audiovisual associations, acquired within a short time and without any feedback, significantly affected the perception of motion direction. This effect was much more salient when the physical direction of visual motion was ambiguous. Moreover, fMRI findings pointed out that the BOLD activities across different cortical regions changed after the associative phase. Conclusion: Taken together, these findings indicate that low-level sensory, multisensory and high-level cognitive areas play a role in the effects of audiovisual associations on motion perception. In general, this suggests that our prior experiences acquired through associations may affect perceptual processing at different hierarchical levels and over different cortical areas.
Open Access
Increasing the spatial extent of attention strengthens surround suppression
(Elsevier Ltd, 2022-10) Kınıklıoğlu, Merve; Boyacı, Hüseyin
Here we investigate how the extent of spatial attention affects center-surround interaction in visual motion processing. To do so, we measured motion direction discrimination thresholds in humans using drifting gratings and two attention conditions. Participants were instructed to limit their attention to the central part of the stimulus under the narrow attention condition, and to both central and surround parts under the wide attention condition. We found stronger surround suppression under the wide attention condition. The magnitude of the attention effect increased with the size of the surround when the stimulus had low contrast, but did not change when it had high contrast. Results also showed that attention had a weaker effect when the center and surround gratings drifted in opposite directions. Next, to establish a link between the behavioral results and the neuronal response characteristics, we performed computer simulations using the divisive normalization model. Our simulations showed that using smaller versus larger multiplicative attentional gain and parameters derived from the medial temporal (MT) area of the cortex, the model can successfully predict the observed behavioral results. These findings reveal the critical role of spatial attention on surround suppression and establish a link between neuronal activity and behavior. Further, these results also suggest that the reduced surround suppression found in certain clinical disorders (e.g., schizophrenia and autism spectrum disorder) may be caused by abnormal attention mechanisms.
Open Access
Specular motion and 3D shape estimation
(Association for Research in Vision and Ophthalmology Inc., 2017) Dövencioğlu, D. N.; Ben-Shahar, O.; Barla, P.; Doerschner, K.
Dynamic visual information facilitates three-dimensional shape recognition. It is still unclear, however, whether the motion information generated by moving specularities across a surface is congruent to that available from optic flow produced by a matte-textured shape. Whereas the latter is directly linked to the firstorder properties of the shape and its motion relative to the observer, the specular flow, the image flow generated by a specular object, is less sensitive to the object's motion and is tightly related to second-order properties of the shape. We therefore hypothesize that the perceived bumpiness (a perceptual attribute related to curvature magnitude) is more stable to changes in the type of motion in specular objects compared with their matte-textured counterparts. Results from two twointerval forced-choice experiments in which observers judged the perceived bumpiness of perturbed spherelike objects support this idea and provide an additional layer of evidence for the capacity of the visual system to exploit image information for shape inference. © 2017 The Authors.