Serial dependence in face-gender classification revealed in low-beta frequency EEG.

Background: Perception depends not only on current sensory input but is also heavily influenced by the immediate past perceptual experience, a phenomenon known as "serial dependence," particularly robust in face perception.

Results: We measured discrimination of face-gender in participants to a sequence of intermingled male, female, and androgynous images, while recording EEG responses. The discriminations showed strong serial dependence (androgynous images biased towards male when preceded by male and female when preceded by female).

Recent, but not long-term, priors induce behavioral oscillations in peri-saccadic vision.

Perception of a continuous world relies on our ability to integrate discontinuous sensory signals when we make saccadic eye movements, which abruptly change the retinal image. Here we investigate the role of oscillations in integrating pre-saccadic information with the current sensory signals. We presented to participants (N = 24) a brief pre-saccadic Gabor stimulus (termed the inducer) before voluntary 16° saccades, followed by a test Gabor stimulus at various times before or after saccadic onset.

Pupillometric signature of implicit learning of statistical regularities.

Animals learn about the statistical regularities of their environment by a process of implicit learning, a powerful mechanism that may operate by mere exposure. Implicit learning supports processes such as speech acquisition but also learning about the spatial and temporal structure of the world more generally, which is essential for effective interaction. Here, we used a frequency-tagging technique to demonstrate a pupillometric signature of the learning of the temporal structure (pairing of numerosities) of sequential arrays.

Color crowding considered as adaptive spatial integration.

Crowding is the inability to recognize an object in clutter, classically considered a fundamental low-level bottleneck to object recognition. Recently, however, it has been suggested that crowding, like predictive phenomena such as serial dependence, may result from optimizing strategies that exploit redundancies in natural scenes. This notion leads to several testable predictions, such as crowding being greater for nonsalient targets and, counterintuitively, that flanker interference should be associated with higher precision in judgements, leading to a lower overall error rate.

Adaptation to numerosity affects the pupillary light response.

We recently showed that the gain of the pupillary light response depends on numerosity, with weaker responses to fewer items. Here we show that this effect holds when the stimuli are physically identical but are perceived as less numerous due to numerosity adaptation. Twenty-eight participants adapted to low (10 dots) or high (160 dots) numerosities and subsequently watched arrays of 10-40 dots, with variable or homogeneous dot size.

Investigating cross-orientation inhibition with continuous tracking.

We investigated cross-orientation inhibition with the recently developed continuous tracking technique. We designed an experiment where participants tracked the horizontal motion of a narrow vertical grating. The target was superimposed on one of three different backgrounds, in separate sessions: a uniform gray background or a sinusoidal grating oriented either parallel or orthogonal to the target.

Serial Dependence in Perception.

Much evidence has shown that perception is biased towards previously presented similar stimuli, an effect recently termed serial dependence. Serial dependence affects nearly every aspect of perception, often causing gross perceptual distortions, especially for weak and ambiguous stimuli. Despite unwanted side-effects, empirical evidence and Bayesian modeling show that serial dependence acts to improve efficiency and is generally beneficial to the system.

The role of neural oscillations in visuo-motor communication at the time of saccades.

Saccadic eye-movements are fundamental for active vision, allowing observers to purposefully scan the environment with the high-resolution fovea. In this brief perspective we outline a series of experiments from our laboratories investigating the role of eye-movements and their consequences to active perception. We show that saccades lead to suppression of visual sensitivity at saccadic onset, and that this suppression is accompanied by endogenous neural oscillations in the delta range.

Autistic individuals show less grouping-induced bias in numerosity judgments.

Introduction: When items are connected together, they tend to be perceived as an integrated whole rather than as individual dots, causing a strong underestimation of the numerosity of the ensemble. Previous evidence on grouping-induced biases of numerosity has shown a dependency on autistic-like personality traits in neurotypical adults, with a weaker tendency for grouping into meaningful segmented objects in individuals with strong autistic traits. Here we asked whether this result would generalize to the autistic population.

The role of non-numerical information in the perception of temporal numerosity.

Numerosity perception refers to the ability to make rapid but approximate estimates of the quantity of elements in a set (spatial numerosity) or presented sequentially (temporal numerosity). Whether numerosity is directly perceived or indirectly recomputed from non-numerical features is a highly debated issue. In the spatial domain, area and density have been suggested as the main parameters through which numerosity would be recomputed.

Serial dependence in orientation judgments at the time of saccades.

We actively seek information from the environment through saccadic eye movements, necessitating continual integration of presaccadic and postsaccadic signals, which are displaced on the retina by each saccade. We tested whether trans-saccadic integration may be related to serial dependence (a measure of how perceptual history influences current perception) by measuring how viewing a presaccadic stimulus affects the perceived orientation of a subsequent test stimulus presented around the time of a saccade. Participants reproduced the position, and orientation of a test stimulus presented around a 16° saccade.

Serial dependence improves performance and biases confidence-based decisions.

Perception depends on both the current sensory input and on the preceding stimuli history, a mechanism referred to as serial dependence (SD). One interesting, and somewhat controversial, question is whether serial dependence originates at the perceptual stage, which should lead to a sensory improvement, or at a subsequent decisional stage, causing solely a bias. Here, we studied the effects of SD in a novel manner by leveraging on the human capacity to spontaneously assess the quality of sensory information.

Evidence of Serial Dependence from Decoding of Visual Evoked Potentials.

It is well known that recent sensory experience influences perception, recently demonstrated by a phenomenon termed "serial dependence." However, its underlying neural mechanisms are poorly understood. We measured ERP responses to pairs of stimuli presented randomly to the left or right hemifield.

Crowding results from optimal integration of visual targets with contextual information.

Crowding is the inability to recognize an object in clutter, usually considered a fundamental low-level bottleneck to object recognition. Here we advance and test an alternative idea, that crowding, like predictive phenomena such as serial dependence, results from optimizing strategies that exploit redundancies in natural scenes. This notion leads to several testable predictions: crowding should be greatest for unreliable targets and reliable flankers; crowding-induced biases should be maximal when target and flankers have similar orientations, falling off for differences around 20°; flanker interference should be associated with higher precision in orientation judgements, leading to lower overall error rate; effects should be maximal when the orientation of the target is near that of the average of the flankers, rather than to that of individual flankers.

Visual priming and serial dependence are mediated by separate mechanisms.

Perceptual history influences current perception, readily revealed by visual priming (the facilitation of responses on repeated presentations of similar stimuli) and by serial dependence (systematic biases toward the previous stimuli). We asked whether the two phenomena shared perceptual mechanisms. We modified the standard "priming of pop-out" paradigm to measure both priming and serial dependence concurrently.

Symmetry as a grouping cue for numerosity perception.

To estimate the number of objects in an image, each element needs to be segregated as a single unit. Several principles guide the process of element identification, one of the strongest being symmetry. In the current study, we investigated how symmetry affects the ability to rapidly estimate the number of objects (numerosity).

Contextual Information Modulates Pupil Size in Autistic Children.

Recent Bayesian models suggest that perception is more "data-driven" and less dependent on contextual information in autistic individuals than others. However, experimental tests of this hypothesis have given mixed results, possibly due to the lack of objectivity of the self-report methods typically employed. Here we introduce an objective no-report paradigm based on pupillometry to assess the processing of contextual information in autistic children, together with a comparison clinical group.

Numerosity perception is tuned to salient environmental features.

Numerosity perception is a key ability to guide behavior. However, current models propose that number units encode an abstract representation of numerosity regardless of the non-numerical attributes of the stimuli, suggesting rather coarse environmental tuning. Here we investigated whether numerosity systems spontaneously adapt to all visible items, or to subsets segregated by salient attributes such as color or pitch.

Ideal observer analysis for continuous tracking experiments.

Continuous tracking is a newly developed technique that allows fast and efficient data acquisition by asking participants to "track" a stimulus varying in some property (usually position in space). Tracking is a promising paradigm for the investigation of dynamic features of perception and could be particularly well suited for testing ecologically relevant situations difficult to study with classical psychophysical paradigms. The high rate of data collection may be useful in studies on clinical populations and children, who are unable to undergo long testing sessions.

Visual Duration but Not Numerosity Is Distorted While Running.

There is increasing evidence that action and perception interact in the processing of magnitudes such as duration and numerosity. Sustained physical exercise (such as running or cycling) increases the apparent duration of visual stimuli presented during the activity. However, the effect of exercise on numerosity perception has not yet been investigated.

Uncertainty and Prior Assumptions, Rather Than Innate Logarithmic Encoding, Explain Nonlinear Number-to-Space Mapping.

Mapping number to space is natural and spontaneous but often nonveridical, showing a clear compressive nonlinearity that is thought to reflect intrinsic logarithmic encoding of numerical values. We asked 78 adult participants to map dot arrays onto a number line across nine trials. Combining participant data, we confirmed that on the first trial, mapping was heavily compressed along the number line, but it became more linear across trials.

The dynamics of grouping-induced biases in apparent numerosity revealed by a continuous tracking technique.

Connecting pairs of items causes robust underestimation of the numerosity of an ensemble, presumably by invoking grouping mechanisms. Here we asked whether this underestimation in numerosity judgments could be revealed and further explored by continuous tracking, a newly developed technique that allows for fast and efficient data acquisition and monitors the dynamics of the responses. Participants continuously reproduced the perceived numerosity of a cloud of dots by moving a cursor along a number line, while the number of dots and the proportion connected by lines varied over time following two independent random walks.

Numbers in action.

To understand the number sense, we need to understand its function. We argue that numerosity estimation is fundamental not only for perception, but also preparation and control of action. We outline experiments that link numerosity estimation with action, pointing to a generalized numerosity system that serves both perception and action preparation.