Swiss National Science Foundation

The Swiss National Science Foundation (SNSF, German: Schweizerischer Nationalfonds zur Förderung der wissenschaftlichen Forschung, SNF; French: Fonds national suisse de la recherche scientifique, FNS; Italian: Fondo nazionale svizzero per la ricerca scientifica) is a science research support organisation mandated by the Swiss Federal Government. The Swiss National Science Foundation was established under private law by physicist and medical doctor Alexander von Muralt in 1952. Organisation The SNSF consists of three main bodies: Foundation Council, National Research Council and Administrative Offices. The Foundation Council is the highest authority and makes strategic decisions. The National Research Council is composed of distinguished researchers who mostly work at Swiss institutions of higher education. They assess research proposals submitted to the SNSF and make funding decisions. The National Research Council comprises up to 100 members and is subdivided into four

Serial dependence under memory load

Gizay Ceylan, Michael Herzog, Yury Markov, Ayberk Ozkirli, David Pascucci, Natalia Tiurina

Perceptual decisions are biased towards previous stimuli, a phenomenon known as serial dependence. However, the mechanisms of this bias are unknown. For example, it is debated whether serial dependence reflects a perceptual bias or interference of prior stimuli in working memory. We addressed this question by testing whether visual working memory load modulates serial dependence. We presented sequences of Gabors appearing at the same or different locations. At the beginning of each sequence, we presented a display with two lines. Participants reproduced the orientation of each of the three Gabors while holding the orientation of the lines in memory. In a control condition, participants reproduced only the orientation of each Gabor, ignoring the lines. Working memory load caused a repulsive bias in the adjustment responses when the previous Gabor was presented at a different location. In the control condition, Gabors at different locations caused no bias at all. When presented at the same location, however, the bias was attractive for small orientation differences (45°), resembling typical serial dependence. Under load, this pattern was qualitatively more pronounced. Our results suggest that working memory load may interact with, rather than prevent, serial dependence by making perceptual decisions more vulnerable to biases. [This research was supported by funding from the Swiss National Science Foundation (grant no. 415 PZ00P1_179988 to DP) and the Swiss Government Excellence Scholarship awarded by Federal Commission for Scholarships for Foreign Students FCS (NT). The funders had no role in the study design, data collection and analysis.]

SAGE Publishing2021

The role of population receptive field size and recurrent processing in learning to “de-crowd”

Bogdan Draganski, Michael Herzog, Maya Anna Jastrzebowska, Ayberk Ozkirli

In crowding, the perception of a target is impeded by surrounding clutter. While traditional models are feedforward and local, there is increasing behavioral and neural evidence for a critical role of recurrent processing across the visual hierarchy in crowding. Our recent fMRI findings suggest that higher visual areas, sensitive to global context, determine whether target and flanker features are combined within a single population receptive field (pRF) or rather the target is separated from the flankers in a smaller pRF, likely through recurrent processing. Here, we investigated the neural correlates of perceptual learning to “de-crowd”. Twelve participants trained on an orientation discrimination task under crowding, with the stimulus always presented in the top-right quadrant. Performance on the crowding condition improved substantially in the trained quadrant, but only to a lesser extent in an untrained quadrant. No significant improvements were seen in a no-crowding condition. We used fMRI to estimate pRF sizes in visual areas V1 to V4, separately in areas representing the four visual quadrants. We used dynamic causal modeling to compare bottom-up, top-down, and recurrent models of learning-related modulation of connectivity between visual areas. We found a substantial decrease in pRF size only in left ventral V3, corresponding to the trained visual quadrant. Learning to de-crowd modulated recurrent connectivity across the visual hierarchy, whereas only bottom-up connectivity was modulated in no-crowding. Our findings suggest that improvements in target discrimination under crowding are mediated by top-down processing, which determines the segmentation of the target and flankers through pRF size adjustment. [We would like to thank our funding sources: Swiss National Science Foundation (NCCR Synapsy, project grant numbers 32003B_135679, 32003B_159780, 324730_192755, CRSK-3_190185, 176153), the Leenaards Foundation, Fondation ROGER DE SPOELBERCH, and the Partridge Foundation.]

SAGE Publishing2021

Population receptive field size in (un)crowding: to isolate or to combine?

Bogdan Draganski, Michael Herzog, Maya Anna Jastrzebowska, Ayberk Ozkirli

Traditional models posit that visual processing is local and feedforward. In this vein, crowding is explained to be the result of pooling of target and flanker features in early visual areas. Specifically, it has been suggested that when the target and flankers fall within the same receptive field, their features are pooled together, resulting in an irreversible loss of information and degraded performance. A recent fMRI study investigated the relation between crowding strength and population receptive field (pRF) sizes (He et al., 2019). The authors reported that stronger crowding coincides with larger pRF sizes in V2, suggesting that pooling occurs in V2. Here, we investigated pRF size in crowding, no crowding and uncrowding, in which adding flankers leads to improvements in target discrimination, contrary to what traditional models of crowding predict. We replicated previous findings of increased pRF size in crowding as compared to no crowding, with pronounced differences throughout early visual areas (V1 to V4, not only V2). Surprisingly, uncrowding coincides with the smallest pRF size, even compared to the no crowding condition, in which behavioral performance is best. Thus, pRF size is modulated by global context and the relationship between pRF size and behavioral performance is non-monotonic. Our findings suggest that pRF size is modulated by top-down feedback, which goes against the classic, purely feedforward models of crowding. We propose that pRFs are the means by which the brain either combines or isolates the target and the flankers – reflected in behavioral performance as crowding and uncrowding, respectively. [We would like to thank our funding sources: Swiss National Science Foundation (176153, http://p3.snf.ch/Project-176153; NCCR Synapsy, project grant numbers 32003B_135679, 32003B_159780, 324730_192755 and CRSK-3_190185), Leenaards Foundation, ROGER DE SPOELBERCH and Partridge Foundations.]

SAGE Publishing2021

The role of population receptive field size and recurrent processing in learning to “de-crowd”

Bogdan Draganski, Michael Herzog, Maya Anna Jastrzebowska, Ayberk Ozkirli

SAGE Publishing2021

Population receptive field size in (un)crowding: to isolate or to combine?

Bogdan Draganski, Michael Herzog, Maya Anna Jastrzebowska, Ayberk Ozkirli

SAGE Publishing2021