https://www.pisavisionlab.org Research centre dedicated to frontier, interdisciplinary research of human perception Tue, 12 Jan 2021 09:00:43 +0000 en-US hourly 1 https://wordpress.org/?v=6.4.13 https://www.pisavisionlab.org/2020/09/24/fast-saccadic-eye-movements-in-humans-suggest-that-numerosity-perception-is-automatic-and-direct-2/ Thu, 24 Sep 2020 13:13:03 +0000 https://www.pisavisionlab.org/?p=3164 Proc. R. Soc. B 287: 20201884. Fast saccades are rapid automatic oculomotor responses to salient and ecologically important visual stimuli such as animals and faces. Discriminating the number of friends, foe, or prey may also have an evolutionary advantage. In this study, participants were asked to saccade rapidly towards the more numerous of two arrays. Participants could discriminate numerosities with high accuracy and great speed, as fast as 190 ms. Intermediate numerosities were more likely to elicit fast saccades than very low or very high numerosities. Reaction-times for vocal responses (collected in a separate experiment) were slower, did not depend on numerical range, and correlated only with the slow not the fast saccades, pointing to different systems. The short saccadic reaction-times we observe are surprising given that discrimination using numerosity estimation is thought to require a relatively complex neural circuit, with several relays of information through the parietal and prefrontal cortex. Our results suggest that fast numerosity-driven saccades may be generated on a single feed-forward pass of information recruiting a primitive system that cuts through the cortical hierarchy and rapidly transforms the numerosity information into a saccade command. Elisa Castaldi, David Burr, Marco Turi and Paola Binda https://doi.org/10.5061/dryad.7d7wm37s6 https://www.pisavisionlab.org/2020/10/09/spontaneous-pupillary-oscillations-increase-during-mindfulness-meditation-2/ Fri, 09 Oct 2020 15:44:45 +0000 https://www.pisavisionlab.org/?p=3273 Current Biology Volume 30, Issue 18, 21 September 2020, Pages R1030-R1031 A significant body of literature has shown that pupil size varies with cognitive and perceptual states [1,2]. Furthermore, the pupil diameter oscillates spontaneously at low frequencies, sometimes referred to as pupillary hippus [3,4]. Oscillation amplitude varies with many neural factors, including arousal and cortical excitability. Here we show that pupillary oscillations are modulated by mindfulness meditation, increasing by 53% compared to pre- and post-meditation baselines. The effect occurs only in trained meditators and is specific for low frequencies (below 1 Hz), with delta frequencies (1–5 Hz) unchanged. The study suggests that pupil size may be a useful marker of the altered cortical state during meditation. Antonella Pome' ; David C. Burr; Analisa Capuozzo; Paola Binda https://doi.org/10.5281/zenodo.3939009 https://www.pisavisionlab.org/2021/01/12/perceptual-history-propagates-down-to-early-levels-of-sensory-analysis-2/ Tue, 12 Jan 2021 08:57:57 +0000 https://www.pisavisionlab.org/?p=3551 Current Biology One function of perceptual systems is to construct and maintain a reliable representation of the environment. A useful strategy intrinsic to modern “Bayesian” theories of perception is to take advantage of the relative stability of the input and use perceptual history (priors) to predict current perception. This strategy is efficient but can lead to stimuli being biased toward perceptual history, clearly revealed in a phenomenon known as serial dependence. However, it is still unclear whether serial dependence biases sensory encoding or only perceptual decisions. We leveraged on the “surround tilt illusion”—where tilted flanking stimuli strongly bias perceived orientation—to measure its influence on the pattern of serial dependence, which is typically maximal for similar orientations of past and present stimuli. Maximal serial dependence for a neutral stimulus preceded by an illusory one occurred when the perceived, not the physical, orientations of the two stimuli matched, suggesting that the priors biasing current perception incorporate the effect of the illusion. However, maximal serial dependence of illusory stimuli induced by neutral stimuli occurred when their physical (not perceived) orientations were matched, suggesting that priors interact with incoming sensory signals before they are biased by flanking stimuli. The evidence suggests that priors are high-level constructs incorporating contextual information, which interact directly with early sensory signals, not with highly processed perceptual representations. Cicchini, Guido Marco; Benedetto, Alessandro; Burr, David https://zenodo.org/record/4362291#.X94jCthKhPY