Discrete confidence levels revealed by sequential decisions.

Humans can meaningfully express their confidence about uncertain events. Normatively, these beliefs should correspond to Bayesian probabilities. However, it is unclear whether the normative theory provides an accurate description of the human sense of confidence, partly because the self-report measures used in most studies hinder quantitative comparison with normative predictions.

Unifying Visual Space Across the Left and Right Hemifields.

Visual space is perceived as continuous and stable even though visual inputs from the left and right visual fields are initially processed separately within the two cortical hemispheres. In the research reported here, we examined whether the visual system utilizes a dynamic recalibration mechanism to integrate these representations and to maintain alignment across the visual fields. Subjects adapted to randomly oriented moving lines that straddled the vertical meridian; these lines were vertically offset between the left and right hemifields.

Time constancy in human perception.

Estimated time contracts or dilates depending on many visual-stimulation attributes (size, speed, etc.). Here we show that when such attributes are jointly modulated so as to respect the rules of perspective, their effect on the perceived duration of moving objects depends on the presence of contextual information about viewing distance.

A Refresher of the Original Bloch's Law Paper (Bloch, July 1885).

In 1885, Adolphe-Moïse Bloch asked the following simple question "Is there a law describing the relationship between the duration of a light and its perceived intensity?" Based on a series of experiments using a Foucault regulator and a candle, Bloch concluded that "when the lighting duration varies from 0.00173 to 0.0518 seconds (…) the [visible] light is markedly in inverse proportion to its duration"-his famous law.

Agency alters perceptual decisions about action-outcomes.

Humans experience themselves as agents, capable of controlling their actions and the outcomes they generate (i.e., the sense of agency).

Temporal frequency of events rather than speed dilates perceived duration of moving objects.

In everyday life moving objects often follow irregular or repetitive trajectories for which distinctive events are potentially noticeable. It is known that the perceived duration of moving objects is distorted, but whether the distortion is due to the temporal frequency of the events or to the speed of the objects remains unclear. Disentangling the contribution of these factors to perceived duration distortions is ecologically relevant: if perceived duration were dependent on speed, it should contract with the distance from the observer to the moving objects.

Time dilates more with apparent than with physical speed.

The perceived duration of a moving stimulus correlates positively with its speed. It is not known whether such duration dilation depends on the physical or apparent speed. Here we show the latter to be true.

Summary statistics for size over space and time.

A number of studies have investigated how the visual system extracts the average feature-value of an ensemble of simultaneously or sequentially delivered stimuli. In this study we model these two processes within the unitary framework of linear systems theory. The specific feature value used in this investigation is size, which we define as the logarithm of a circle's diameter.

A unified comparison of stimulus-driven, endogenous mandatory and 'free choice' saccades.

It has been claimed that saccades arising from the three saccade triggering modes-stimulus-driven, endogenous mandatory and 'free choice'-are driven by distinct mechanisms. We tested this claim by instructing observers to saccade from a white or black fixation disc to a same polarity (white or black) disc flashed for 100 or 200 ms presented either alone (Exo), or together with an opposite (Endo) or same (EndoFC) polarity disc (blocked and mixed sessions). Target(s) and distractor were presented at three inter-stimulus intervals (ISIs) relative to the fixation offset (ISI: -200, 0, +200 ms) and were displayed at random locations within a 4°-to-6° eccentricity range.

Time in perspective.

Perceptions of time and space are subject to strong contextual effects. Like their physical counterparts, they appear to be bound together. The perceived spatial extent of a constant retinal extent increases with its perceived distance from the observer.

Recognition criteria vary with fluctuating uncertainty.

In distinct experiments we examined memories for orientation and size. After viewing a randomly oriented Gabor patch (or a plain white disk of random size), observers were given unlimited time to reproduce as faithfully as possible the orientation (or size) of that standard stimulus with an adjustable Gabor patch (or disk). Then, with this match stimulus still in view, a recognition probe was presented.

Decision criteria in dual discrimination tasks estimated using external-noise methods.

According to classical signal detection theory (SDT), in simple detection or discrimination tasks, observers use a decision parameter based on their noisy internal response to set a boundary between "yes" and "no" responses. Experimental paradigms where performance is limited by internal noise cannot be used to provide an unambiguous measure of the decision criterion and its variability. Here, unidimensional external noise is used to estimate a criterion and its variability in stimulus space.

Ticks per thought or thoughts per tick? A selective review of time perception with hints on future research.

The last decade underwent a revival of interest in the perception of time and duration. The present short essay does not compete with the many other recent reviews and books on this topic. Instead, it is meant to emphasize the notion that humans (and most likely other animals) have at their disposal more than one time measuring device and to propose that they use these devices jointly to appraise the passage of time.

Location and identity memory of saccade targets.

While the memory of objects' identity and of their spatiotopic location may sustain transsaccadic spatial constancy, the memory of their retinotopic location may hamper it. Is it then true that saccades perturb retinotopic but not spatiotopic memory? We address this issue by assessing localization performances of the last and of the penultimate saccade target in a series of 2-6 saccades. Upon fixation, nine letter-pairs, eight black and one white, were displayed at 3° eccentricity around fixation within a 20° × 20° grey frame, and subjects were instructed to saccade to the white letter-pair; the cycle was then repeated.

On the perceptual/motor dissociation: a review of concepts, theory, experimental paradigms and data interpretations.

With its roots in Ungerleider and Mishkin's (1982) uncovering of two distinct - ventral and dorsal - anatomical pathways for the processing of visual information, and boosted by Goodale and Milner's (1992; Milner and Goodale, 1995) behavioral study of patients with lesions of either of these pathways, the perception-action dissociation became a standard reference in the sensorimotor literature. Here we present briefly the anatomical, neuropsychological and, more extensively, the psychophysical evidence favoring such dissociation and pit it against counteracting evidence as well as against potential methodological and conceptual pitfalls. We also discuss classes of models accounting for a number of 'dissociation' results and conclude that the most general and parsimonious one posits the existence of one single processing stream that accumulates information up to a decision criterion modulated by stimulation conditions, response mode (motor vs.

Introspective duration estimation of reactive and proactive motor responses.

The metajudgment of motor responses refers to our ability to evaluate the accuracy of our own actions. Can humans metajudge the duration of their Reaction Times (RTs) to a light-flash and the accuracy of their reproduction of a reference time interval bounded by two light flashes (Anticipatory Response Time, ART)? A series of four distinct experiments shows that RT_Meta and ART_Metajudgments are possible but with accuracies about x2.4 and x3 poorer than the corresponding RT and ART ones.

Adaptation and prolonged inhibition as a main cause of motion-induced blindness.

Motion-induced blindness (MIB) is one of the most enigmatic perceptual disappearance phenomena. Here we suggest that MIB may be caused by the combined effects of two distinct adaptation processes: one shared with two other non-MIB configurations and entailing a response-gain reduction, and a second, MIB-specific transient-to-sustained incremental inhibition causing a contrast-gain reduction. Response-gain reduction is evidenced by brightness-tracking experiment where the 1-minute brightness time course of an MIB target is compared to the time courses of the same target superimposed on a static mask (SM) and on no mask at all (absent mask; AM).

Comparison of perceptual and motor latencies via anticipatory and reactive response times.

To compare the timing of perceptual and motor decisions, distinct tasks have been designed, all of which have yielded systematic differences between these two moments. These observations have been taken as evidence of a sensorimotor dissociation. Inasmuch as the distinction between perceptual and motor decision moments is conceptually warranted, this conclusion remains debatable, since the observed differences may reflect the dissimilarity between the stimulations/tasks used to assess them.

Comparison of perceptual and motor decisions via confidence judgments and saccade curvature.

This study investigated the effects on perceptual and motor decisions of low-contrast distractors, presented 5 degrees on the left and/or the right of the fixation point. Perceptual decisions were assessed with a yes/no (distractor) detection task. Motor decisions were assessed via these distractors' effects on the trajectory of an impending saccade to a distinct imperative stimulus, presented 10 degrees above fixation 50 ms after the distractor(s).

When they see, they see it almost right: normal subjective experience of detected stimuli in spatial neglect.

Unilateral spatial neglect (USN) patients show reduced contrast sensitivity on their contralesional side and often miss their non-salient stimuli. What their subjective experience is when successfully reporting a stimulus remains unclear. Here, we report that despite large contrast sensitivity differences between the sides, the relative attenuation in perceived contrast measured in a contrast-matching task was small.

Investigation of perceptual constancy in the temporal-envelope domain.

The ability to discriminate complex temporal envelope patterns submitted to temporal compression or expansion was assessed in normal-hearing listeners. An XAB, matching-to-sample-procedure was used. X, the reference stimulus, is obtained by applying the sum of two, inharmonically related, sinusoids to a broadband noise carrier.

Sensory and decisional factors in motion-induced blindness.

The processes underlying motion-induced blindness (MIB) are widely debated. Ultimately, however, they must reduce to a sensitivity drop and/or to an upward shift of the decision criterion. The first possibility was tested by assessing the detection threshold for a contrast (or luminance) increment applied to the MIB target under its visible and suppressed phases.

Temporal order judgment and simple reaction times: evidence for a common processing system.

We present a simple reaction time (RT) versus temporal order judgment (TOJ) experiment as a test of the perception-action relationship. The experiment improves on previous ones in that it assesses for the first time RT and TOJ on a trial-by-trial basis, hence allowing the study of the two behaviors within the same task context and, most importantly, the association of RT to "correct" and "incorrect" TOJs. RTs to pairs of stimuli are significantly different depending on the associated TOJs, an indication that perceptual and motor decisions are based on the same internal response.

Perceptual criterion and motor threshold: a signal detection analysis of the relationship between perception and action.

Although a large number of studies have demonstrated that a motor response to a visual stimulus is, at least to some extent, independent of the perceptual response, little effort has been spent on the investigation of the explicit characteristics of this independency. In the present experiment, observers were presented with an S1-S2 stimulus-pair, with S1 within the threshold range and with S2 highly suprathreshold. S2 was displayed either at the same location as S1 (masked condition), or some degree to the left or right of S1 (non-masked).