Researcher: Karşılar, Hakan
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Karşılar, Hakan
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Publication Metadata only Asymmetrical modulation of time perception by increase versus decrease in coherence of motion(Springer, 2016) N/A; N/A; Department of Psychology; Karşılar, Hakan; Balcı, Fuat; PhD Student; Faculty Member; Department of Psychology; Graduate School of Social Sciences and Humanities; College of Social Sciences and Humanities; 291441; 51269Stimulus properties are known to affect duration judgments. In this study, we tested the effect of motion coherence levels in randomly moving dots on the perceived duration of these stimuli. In Experiments 1 and 2 we tested participants on a temporal reproduction task, using stimuli with varying degrees of motion coherence as the to-be-timed stimuli. Our results in both experiments showed that increasing motion coherence from the encoded (i.e. the first) to the reproduced (i.e. the second) stimulus leads to longer reproduction times. These effects were primarily additive in nature, and their magnitude increased with the difference between the coherence levels in the encoding versus reproduction (decoding) phases. This effect was not mirrored when there was a decrease in motion coherence. Experiment 3 tested if the differential number of exploratory saccadic eye-movements during encoding and reproduction predicted these effects. The behavioral findings of Experiment 1 and 2 were replicated in the third experiment, and the change in the number of eye movements from encoding to reproduction predicted the reproduction time when there was an increase in motion coherence. These results are explained by the effect of attention on the latency to initiate temporal integration that is only manifested when there is an increase in the level of motion coherence.Publication Metadata only Symbolism overshadows the effect of physical size in supra-second temporal illusions(Springer, 2019) N/A; N/A; Department of Psychology; Karşılar, Hakan; Balcı, Fuat; PhD Student; Faculty Member; Department of Psychology; Graduate School of Social Sciences and Humanities; College of Social Sciences and Humanities; 291441; 51269The perception of quantities has been suggested to rely on shared, magnitude-based representational systems that preserve metric properties. As such, different quantifiable dimensions that can characterize any given stimulus (e.g., size, speed, or numerosity) have been shown to modulate the perceived duration of these stimuli-a finding that has been attributed to cross-modal interaction among the quantity representations. However, these results are typically based on the isolated effects of a single stimulus dimension, leaving their potential combined effects uncharted. In the present study we aimed to investigate the joint effects of numerical magnitude and physical size on perceived time. In four complementary experiments, participants categorized six durations as "short" or "long," which were presented through combinations of Hindu-Arabic numerals in three font sizes, as well as with simple shapes (rectangles) and unfamiliar symbols (Klingon letters), the sizes of which corresponded to the font sizes of the Hindu-Arabic numerals. Our results showed temporal underestimation for the smallest numeral in the set (3), with no effects of font size on perceived duration. The perceived durations were longest for the physically smallest geometric stimuli (i.e., a rectangle), and the font size of symbol-like stimuli (i.e., Klingon letters) was not found to have an effect on perceived time. Finally, presenting only one numeral (6) instead of the rectangle once again eliminated the relationship between physical size and perceived time, suggesting an overshadowing of physical-size-based influences on temporal choice behavior, presumably by perceived symbolism. Our results point at the complex nature of the interaction between different magnitude representations.Publication Metadata only Speed accuracy trade-off under response deadlines(Frontiers, 2014) Simen, Patrick; Papadakis, Samantha; N/A; Department of Psychology; Karşılar, Hakan; Balcı, Fuat; PhD Student; Faculty Member; Department of Psychology; Graduate School of Social Sciences and Humanities; College of Social Sciences and Humanities; 291441; 51269Perceptual decision making has been successfully modeled as a process of evidence accumulation up to a threshold. In order to maximize the rewards earned for correct responses in tasks with response deadlines, participants should collapse decision thresholds dynamically during each trial so that a decision is reached before the deadline. This strategy ensures on-time responding, though at the cost of reduced accuracy, since slower decisions are based on lower thresholds and less net evidence later in a trial (compared to a constant threshold). Frazier & Yu (2008) showed that the normative rate of threshold reduction depends on deadline delays and on participants' uncertainty about these delays. Participants should start collapsing decision thresholds earlier when making decisions under shorter deadlines (for a given level of timing uncertainty) or when timing uncertainty is higher (for a given deadline). We tested these predictions using human participants in a random dot motion discrimination task. Each participant was tested in free-response, short deadline (800 ms), and long deadline conditions (1000 ms). Contrary to optimal-performance predictions, the resulting empirical function relating accuracy to response time (RT) in deadline conditions did not decline to chance level near the deadline; nor did the slight decline we typically observed relate to measures of endogenous timing uncertainty. Further, although this function did decline slightly with increasing RT, the decline was explainable by the best-fitting parameterization of Ratcliff's diffusion model (Ratcliff, 1978), whose parameters are constant within trials. Our findings suggest that at the very least, typical decision durations are too short for participants to adapt decision parameters within trials.Publication Open Access Speed accuracy trade-off under response deadlines(Elsevier, 2014) Simen, Patrick; Papadakis, Samantha; Department of Psychology; Balcı, Fuat; Karşılar, Hakan; Faculty Member; Department of Psychology; College of Social Sciences and Humanities; 51269; N/AThe majority of two-alternative forced choice (2AFC) psychophysics studies have examined speed-accuracy trade-offs either in free-response or fixed viewing time paradigms with no hard time constraints on responding. Under response deadlines, reward maximization requires participants to modulate decision thresholds over the course of a trial such that when the deadline arrives a response is ensured despite the possible reduction of accuracy to the chance level. Importantly, this normative threshold collapsing process should take account not only of the deadline time but also the participants’ level of timing uncertainty about the deadline. For instance, for a given level of timing uncertainty participants facing a more stringent deadline and for a given deadline participants with higher timing uncertainty should start collapsing thresholds earlier within a trial(Frazier, P., & Yu, A. J. (2008). Sequential hypothesis testing under stochastic deadlines.Advances In Neural Information Processing Systems, 20, 465-472). We tested human participants in random dot motion discrimination task in three different conditions: free-response paradigm and with two different response deadlines (800 and 1000 ms). We also quantified the level of timing uncertainty using two different temporal reproduction tasks. Micro speed-accuracy trade-off curves suggested that participants might have collapsed thresholds within a trial when facing a response deadline; however, observed performance diverged markedly from optimality. Participants did not take account of either response deadline times or their timing uncertainty. Our findings define a limit on the optimal temporal risk assessment performance of humans. We also consider other possible sources of observed reduction in accuracy as response times approach the deadline, through simulations of data using empirical model parameters.Publication Open Access Dilation and constriction of subjective time based on observed walking speed(Frontiers, 2018) Department of Psychology; Karşılar, Hakan; Kısa, Yağmur Deniz; Balcı, Fuat; Faculty Member; Department of Psychology; Graduate School of Social Sciences and Humanities; N/A; N/A; 51269The physical properties of events are known to modulate perceived time. This study tested the effect of different quantitative (walking speed) and qualitative (walking-forward vs. walking-backward) features of observed motion on time perception in three complementary experiments. Participants were tested in the temporal discrimination (bisection) task, in which they were asked to categorize durations of walking animations as "short" or "long." We predicted the faster observed walking to speed up temporal integration and thereby to shift the point of subjective equality leftward, and this effect to increase monotonically with increasing walking speed. To this end, we tested participants with two different ranges of walking speeds in Experiment 1 and 2 and observed a parametric effect of walking speed on perceived time irrespective of the direction of walking (forward vs. rewound forward walking). Experiment 3 contained a more plausible backward walking animation compared to the rewound walking animation used in Experiments 1 and 2 (as validated based on independent subjective ratings). The effect of walking-speed and the lack of the effect of walking direction on perceived time were replicated in Experiment 3. Our results suggest a strong link between the speed but not the direction of perceived biological motion and subjective time.