Visuo-motor updating in individuals with heightened autistic traits.

Autism spectrum disorder (ASD) presents a range of challenges, including heightened sensory sensitivities. Here, we examine the idea that sensory overload in ASD may be linked to issues with efference copy mechanisms, which predict the sensory outcomes of self-generated actions, such as eye movements. Efference copies play a vital role in maintaining visual and motor stability. Disrupted efference copies hinder precise predictions, leading to increased reliance on actual feedback and potential distortions in perceptions across eye movements. In our first experiment, we tested how well healthy individuals with varying levels of autistic traits updated their mental map after making eye movements. We found that those with more autistic traits had difficulty using information from their eye movements to update the spatial representation of their mental map, resulting in significant errors in object localization. In the second experiment, we looked at how participants perceived an object displacement after making eye movements. Using a trans-saccadic spatial updating task, we found that those with higher autism scores exhibited a greater bias, indicating under-compensation of eye movements and a failure to maintain spatial stability during saccades. Overall, our study underscores efference copy's vital role in visuo-motor stability, aligning with Bayesian theories of autism, potentially informing interventions for improved action-perception integration in autism.

Prediction of sensorimotor contingencies generates saccadic omission.

With every movement of our eyes, the visual receptors in the retina are swiped across the visual scene. Saccades are the fastest and most frequent movements we perform, yet we remain unaware of the self-produced visual motion. Previous research has tried to identify a dedicated suppression mechanism that either actively or passively cancels vision at the time of saccades.1 Here, we investigated a novel theory, which states that saccadic omission results from habituation to the predicted sensory consequences of our own actions. We experimentally induced novel, i.e., artificial visual consequences of saccade performance by presenting gratings that were drifting faster than the flicker fusion frequency and that became visible only when participants performed saccades. We asked participants to perform more than 100 saccades in each session across these gratings to make the novel contingencies predictable for the sensorimotor system. We found that contrast sensitivity for intra-saccadic motion declined drastically after repeated exposure of such motion. The reduction in sensitivity was even specific to the saccade vector performed in habituation trials. Moreover, when subjects performed the same task in fixation, no reduction in sensitivity was observed. In a motion speed comparison task, we found that the reduction in contrast sensitivity is the consequence of silencing-predicted intra-saccadic visual motion. Our data demonstrate that the sensorimotor system selectively habituates to recurring intra-saccadic visual motion, suggesting an efficient prediction mechanism of visual stability.

Altered oculomotor flexibility is linked to high autistic traits.

Autism is a multifaced disorder comprising sensory abnormalities and a general inflexibility in the motor domain. The sensorimotor system is continuously challenged to answer whether motion-contingent errors result from own movements or whether they are due to external motion. Disturbances in this decision could lead to the perception of motion when there is none and to an inflexibility with regard to motor learning. Here, we test the hypothesis that altered processing of gaze-contingent sensations are responsible for both the motor inflexibility and the sensory overload in autism. We measured motor flexibility by testing how strong participants adapted in a classical saccade adaptation task. We asked healthy participants, scored for autistic traits, to make saccades to a target that was displaced either in inward or in outward direction during saccade execution. The amount of saccade adaptation, that requires to shift the internal target representation, varied with the autistic symptom severity. The higher participants scored for autistic traits, the less they adapted. In order to test for visual stability, we asked participants to localize the position of the saccade target after they completed their saccade. We found the often-reported saccade-induced mis-localization in low Autistic Quotient (AQ) participants. However, we also found mislocalization in high AQ participants despite the absence of saccade adaptation. Our data suggest that high autistic traits are associated with an oculomotor inflexibility that might produce altered processing of trans-saccadic vision which might increase the perceptual overstimulation that is experienced in autism spectrum disorders (ASD).

Motor recalibration of visual and saccadic maps.

How does the brain maintain an accurate visual representation of external space? Movement errors following saccade execution provide sufficient information to recalibrate motor and visual space. Here, we asked whether spatial information for vision and saccades is processed in shared or in separate resources. We used saccade adaptation to modify both, saccade amplitudes and visual mislocalization. After saccade adaptation was induced, we compared participants' saccadic and perceptual localization before and after we inserted 'no error' trials. In these trials, we clamped the post-saccadic error online to the predicted endpoints of saccades. In separate experiments, we either annulled the retinal or the prediction error. We also varied the number of 'no error' trials across conditions. In all conditions, we found that saccade adaptation remained undisturbed by the insertion of 'no error' trials. However, mislocalization decreased as a function of the number of trials in which zero retinal error was displayed. When the prediction error was clamped to zero, no mislocalization was observed at all. The results demonstrate the post-saccadic error is used separately to recalibrate visual and saccadic space.

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. After validating in neurotypical adults a child-friendly pupillometric paradigm, in which we embedded test images within an animation movie that participants watched passively, we compared pupillary response to images of the sun and meaningless control images in children with autism vs. age- and IQ-matched children presenting developmental disorders unrelated to the autistic spectrum. Both clinical groups showed stronger pupillary constriction for the sun images compared with control images, like the neurotypical adults. However, there was no detectable difference between autistic children and the comparison group, despite a significant difference in pupillary light responses, which were enhanced in the autistic group. Our report introduces an objective technique for studying perception in clinical samples and children. The lack of statistically significant group differences in our tests suggests that autistic children and the comparison group do not show large differences in perception of these stimuli. This opens the way to further studies testing contextual processing at other levels of perception.

Grouping-Induced Numerosity Biases Vary with Autistic-Like Personality Traits.

Individuals with autism spectrum disorder are thought to have a more local than global perceptual style. We used a novel paradigm to investigate how grouping-induced response biases in numerosity judgments depend on autistic-like personality traits in neurotypical adults. Participants judged the numerosity of clouds of dot-pairs connected by thin lines, known to cause underestimation of numerosity. The underestimation bias correlated strongly with autism-spectrum quotient (r = 0.72, Bayes factor > 100), being weaker for participants with high autistic traits. As connecting dots probably activates global grouping mechanisms, causing dot-pairs to be processed as an integrated whole rather than as individual dots, the results suggest that these grouping mechanisms may be weaker in individuals self-reporting high levels of autistic-like traits.

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. The technique was robust and efficient, and correlated well with results obtained with a standard psychophysics task. Connecting objects with lines caused an underestimation of approximately 15% during tracking, agreeing with previous studies. The response to the lines was slower than the response to the physical numerosity, with a delay of approximately 150 ms, suggesting that this extra time is necessary for processing the grouping effect.

The Grouping-Induced Numerosity Illusion Is Attention-Dependent.

Perceptual grouping and visual attention are two mechanisms that help to segregate visual input into meaningful objects. Here we report how perceptual grouping, which affects perceived numerosity, is reduced when visual attention is engaged in a concurrent visual task. We asked participants to judge the numerosity of clouds of dot-pairs connected by thin lines, known to cause underestimation of numerosity, while simultaneously performing a color conjunction task. Diverting attention to the concomitant visual distractor significantly reduced the grouping-induced numerosity biases. Moreover, while the magnitude of the illusion under free viewing covaried strongly with AQ-defined autistic traits, under conditions of divided attention the relationship was much reduced. These results suggest that divided attention modulates the perceptual grouping of elements by connectedness and that it is independent of the perceptual style of participants.

The pupil responds spontaneously to perceived numerosity.

Although luminance is the main determinant of pupil size, the amplitude of the pupillary light response is also modulated by stimulus appearance and attention. Here we ask whether perceived numerosity modulates the pupillary light response. Participants passively observed arrays of black or white dots of matched physical luminance but different physical or illusory numerosity. In half the patterns, pairs of dots were connected by lines to create dumbbell-like shapes, inducing an illusory underestimation of perceived numerosity; in the other half, connectors were either displaced or removed. Constriction to white arrays and dilation to black were stronger for patterns with higher perceived numerosity, either physical or illusory, with the strength of the pupillary light response scaling with the perceived numerosity of the arrays. Our results show that even without an explicit task, numerosity modulates a simple automatic reflex, suggesting that numerosity is a spontaneously encoded visual feature.

Location- and object-based attention enhance number estimation.

Humans and non-humans can extract an estimate of the number of items in a collection very rapidly, raising the question of whether attention is necessary for this process. Visual attention operates in various modes, showing selectivity both to spatial location and to objects. Here, we tested whether each form of attention can enhance number estimation, by measuring whether presenting a visual cue to increase attentional engagement will lead to a more accurate and precise representation of number, both when attention is directed to location and when it is directed to objects. Results revealed that enumeration of a collection of dots in the location previously cued led to faster, more precise, and more accurate judgments than enumeration in un-cued locations, and a similar benefit was seen when the cue and collection appeared on the same object. This work shows that like many other perceptual tasks, numerical estimation may be enhanced by the spread of active attention inside a pre-cued object.

Spontaneous pupillary oscillations increase during mindfulness meditation.

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.

Pupillometry correlates of visual priming, and their dependency on autistic traits.

In paradigms of visual search where the search feature (say color) can change from trial to trials, responses are faster for trials where the search color is repeated than when it changes. This is a clear example of "priming" of attention. Here we test whether the priming effects can be revealed by pupillometry, and also whether they are related to autistic-like personality traits, as measured by the Autism-Spectrum Quotient (AQ). We repeated Maljkovic and Nakayama's (1994) classic priming experiment, asking subjects to identify rapidly the shape of a singleton target defined by color. As expected, reaction times were faster when target color repeated, and the effect accumulated over several trials; but the magnitude of the effect did not correlate with AQ. Reaction times were also faster when target position was repeated, again independent of AQ. Presentation of stimuli caused the pupil to dilate, and the magnitude of dilation was greater for switched than repeated trials. This effect did not accumulate over trials, and did not correlate with the reaction times difference, suggesting that the two indexes measure independent aspects of the priming phenomenon. Importantly, the amplitude of pupil modulation correlated negatively with AQ, and was significant only for those participants with low AQ. The results confirm that pupillometry can track perceptual and attentional processes, and furnish useful information unobtainable from standard psychophysics, including interesting dependencies on personality traits.

Higher attentional costs for numerosity estimation at high densities.

Humans can estimate numerosity over a large range, but the precision with which they do so varies considerably over that range. For very small sets, within the subitizing range of up to about four items, estimation is rapid and errorless. For intermediate numerosities, errors vary directly with the numerosity, following Weber's law, but for very high numerosities, with very dense patterns, thresholds continue to rise with the square root of numerosity. This suggests that three different mechanisms operate over the number range. In this study we provide further evidence for three distinct numerosity mechanisms, by studying their dependence on attentional resources. We measured discrimination thresholds over a wide range of numerosities, while manipulating attentional load with both visual and auditory dual tasks. The results show that attentional effects on thresholds vary over the number range. Both visual and auditory attentional loads strongly affect subitizing, much more than for larger numerosities. Attentional costs remain stable over the estimation range, then rise again for very dense patterns. These results reinforce the idea that numerosity is processed by three separates but probably overlapping systems.

Different reaction-times for subitizing, estimation, and texture.

Humans can estimate and encode numerosity over a large range, from very few items to several hundreds. Two distinct mechanisms have been proposed: subitizing, for numbers up to four and estimation for larger numerosities. We have recently extended this idea by suggesting that for very densely packed arrays, when items are less segregable, a third "texture" mechanism comes into play. In this study, we provide further evidence for the existence of a third regime for numerosity. Reaction times were very low in the subitizing range, rising rapidly for numerosities greater than four. However, for tightly packed displays of very high numerosities, reaction times became faster. These results reinforce the idea of three regimes in the processing of numerosity, subitizing, estimation, and texture.

Postoperative cognitive dysfunction and short-term neuroprotection from blueberries: a pilot study.

BACKGROUND: General anesthesia may be a risk factor for post-operative cognitive impairment, which could be counteracted by neuroprotective compounds. The aims of this study were to determine cognitive functions impaired by general anesthesia and to test blueberry juice as a neuroprotective agent against neuropsychological dysfunctions induced by general anesthesia. METHODS: Twenty-six patients undergoing elective major surgery were randomized into two groups, receiving either 500 mL/day of blueberry juice within 14 preoperative days (G1) or to a control group (G0). Neuropsychological tests were performed around 20 days before surgery (T0), as well as both three hours (T1) and 24 hours (T2) after surgery. All the scores were statistically analyzed to find significant differences between groups and within the three times. RESULTS: The control (G0) group showed a significant decrease in the performance in the Prose Memory Test (P<0.001), the Attentional Matrices Test (P<0.01), and the Trail Making Test Part B (P<0.01) after general anesthesia. Significant differences were reported in the Prose Memory test, T0 versus T1 (P<0.01), T0 versus T2 (P<0.001); in the Trail Making Test Part B, T0 versus T2 (P<0.01); and the Attentional Matrices test, and T0 versus T2 (P<0.001). The G1 group did not show any decrease in the performance of the three tests. CONCLUSIONS: General anesthesia induces a short-term impairment of verbal memory and selective and divided attention. Blueberry compounds may prevent these neuropsychological deficits through a neuroprotective action in patients undergoing general anesthesia.