The development of speed discrimination abilities

Developmental change in predictive motor abilities

Prediction is critical for successful interactions with a dynamic environment. To test the development of predictive processes over the life span, we designed a suite of interceptive tasks implemented as interactive video games. Four tasks involving interactions with a flying ball with titrated challenge quantified spatiotemporal aspects of prediction. For comparison, reaction time was assessed in a matching task. The experiments were conducted in a museum, where over 400 visitors across all ages participated, and in a laboratory with a focused age group. Results consistently showed that predictive ability improved with age to reach adult level by age 12. In contrast, reaction time continued to decrease into late adolescence. Inter-task correlations revealed that the tasks tested different aspects of predictive processes. This developmental progression complements recent findings on cerebellar and cortical maturation. Additionally, these results can serve as normative data to study predictive processes in individuals with neurodevelopmental conditions.

Incentive motivation improves numerosity discrimination in children and adolescents

We recently showed that incentive motivation improves the precision of the Approximate Number System (ANS) in young adults. To shed light on the development of incentive motivation, the present study investigated whether this effect and its underlying mechanisms may also be observed in younger samples. Specifically, seven-year-old children (n = 23; 12 girls) and 14-year-old adolescents (n = 30; 15 girls) performed a dot comparison task with monetary reward incentives. Both age groups showed higher accuracy in a reward compared to a neutral condition and, similarly, higher processing efficiency as revealed by the drift rate parameter of the EZ-diffusion model. Furthermore, in line with the Incentive Salience Hypothesis, phasic pupil dilations—indicating the activation of the brain’s salience network—were greater in incentivized trials in both age groups. Together these finding suggest that incentive modulation improves numerosity discrimination in children and adolescents by enhancing the perceptual saliency of numerosity information. However, the observed reward anticipation effects were less pronounced in children relative to adolescents. Furthermore, unlike previous findings regarding young adults, the decision thresholds of children and adolescents were not raised by the monetary reward, which may indicate a more protracted development of incentive regulation of response caution than perceptual evidence accumulation.

Grading reliability of the tear film viscosity examination

PURPOSE

To assess the reliability of a tear film (TF) viscosity video grading system.

METHODS

Thirty-four dynamic TF viscosity videos were obtained by a clinically available TF analyzer and objectively sorted according to the movement speed of three arbitrary reflective light particles. A 4-grade system was constructed on a specially designed window for simultaneous comparison with the three standard videos. Two masked graders were invited to grade these videos under a randomized procedure. Observer reliabilities were determined by Spearman's correlation analysis and Bland-Altman agreement analysis.

RESULTS

For this four-grade system, the intra-observer correlation was very strong in the two graders (ρ = 0.96 and 0.82; both P < 0.0001). However, the inter-observer correlation showed moderate strength in normal playback speed (ρ = 0.53, P = 0.002 and ρ = 0.52, P = 0.003 for 1st and 2nd gradings, respectively). In slower playback videos, the inter-observer correlation of the two graders was higher (ρ = 0.70 and P < 0.0001) when reduced to 0.8-times playback speed. Moreover, the 0.8-times mode was also significantly better than normal playback mode (P = 0.0204) in terms of inter-observer agreement.

CONCLUSIONS

The dynamic 4-grade system has an excellent intra-observer reliability and a good inter-observer reliability under 0.8-times playback speed. The grading system established in this study provides a promising solution for rapidly determining the level of TF viscosity.

Deficits in higher visual area representations in a mouse model of Angelman syndrome

Background

Sensory processing deficits are common in individuals with neurodevelopmental disorders. One hypothesis is that deficits may be more detectable in downstream, “higher” sensory areas. A mouse model of Angelman syndrome (AS), which lacks expression of the maternally inherited Ube3a allele, has deficits in synaptic function and experience-dependent plasticity in the primary visual cortex. Thus, we hypothesized that AS model mice have deficits in visually driven neuronal responsiveness in downstream higher visual areas (HVAs).

Methods

Here, we used intrinsic signal optical imaging and two-photon calcium imaging to map visually evoked neuronal activity in the primary visual cortex and HVAs in response to an array of stimuli.

Results

We found a highly specific deficit in HVAs. Drifting gratings that changed speed caused a strong response in HVAs in wildtype mice, but this was not observed in littermate AS model mice. Further investigation with two-photon calcium imaging revealed the effect to be largely driven by aberrant responses of inhibitory interneurons, suggesting a cellular basis for higher level, stimulus-selective cortical dysfunction in AS.

Conclusion

Assaying downstream, or “higher” circuitry may provide a more sensitive measure for circuit dysfunction in mouse models of neurodevelopmental disorders.

Trial registration

Not applicable.

Effect of Visual Field Location on Global Motion Perception: A Developmental Study

Previous work has shown that motion perception in school-age children is similar to that of adults for fast speeds but is immature at slow speeds for stimuli presented in the central visual field. This study examined whether visual field location affects this developmental pattern. We measured left/right and up/down global motion direction discrimination for fast and slow speeds in 7- to 10-year-old children and in adults with stimuli presented to upper, central, or lower visual fields. For left/right direction discrimination, children showed significantly higher (worse) coherence thresholds than adults for slow, but not fast, speeds in the central visual field. In the upper and lower visual fields, children showed significantly higher coherence thresholds than adults for both speeds. For up/down direction discrimination, children showed similar performance to adults for the central visual field. In the upper and lower visual fields, children performed significantly worse than adults; this finding was speed-tuned only for the lower visual field. Thus, children show immature global motion perception in the periphery even when performance in central vision is adult-like. These results enrich our understanding of motion perception development in children with typical vision.

Perceptual Decision-Making in Children: Age-Related Differences and EEG Correlates

Children make faster and more accurate decisions about perceptual information as they get older, but it is unclear how different aspects of the decision-making process change with age. Here, we used hierarchical Bayesian diffusion models to decompose performance in a perceptual task into separate processing components, testing age-related differences in model parameters and links to neural data. We collected behavioural and EEG data from 96 6- to 12-year-old children and 20 adults completing a motion discrimination task. We used a component decomposition technique to identify two response-locked EEG components with ramping activity preceding the response in children and adults: one with activity that was maximal over centro-parietal electrodes and one that was maximal over occipital electrodes. Younger children had lower drift rates (reduced sensitivity), wider boundary separation (increased response caution) and longer non-decision times than older children and adults. Yet, model comparisons suggested that the best model of children's data included age effects only on drift rate and boundary separation (not non-decision time). Next, we extracted the slope of ramping activity in our EEG components and covaried these with drift rate. The slopes of both EEG components related positively to drift rate, but the best model with EEG covariates included only the centro-parietal component. By decomposing performance into distinct components and relating them to neural markers, diffusion models have the potential to identify the reasons why children with developmental conditions perform differently to typically developing children and to uncover processing differences inapparent in the response time and accuracy data alone.

Development of visual perception of others' actions: Children's judgment of lifted weight

Humans are excellent at perceiving different features of the actions performed by others. For instance, by viewing someone else manipulating an unknown object, one can infer its weight–an intrinsic feature otherwise not directly accessible through vision. How such perceptual skill develops during childhood remains unclear. To confront this gap, the current study had children (N:63, 6–10 years old) and adults (N:21) judge the weight of objects after observing videos of an actor lifting them. Although 6-year-olds could already discriminate different weights, judgment accuracy had not reached adult-like levels by 10 years of age. Additionally, children’s stature was a more reliable predictor of their ability to read others’ actions than was their chronological age. This paper discusses the results in light of a potential link between motor development and action perception.

Neural dynamics underlying coherent motion perception in children and adults

Motion sensitivity increases during childhood, but little is known about the neural correlates. Most studies investigating children's evoked responses have not dissociated direction-specific and non-direction-specific responses. To isolate direction-specific responses, we presented coherently moving dot stimuli preceded by incoherent motion, to 6- to 7-year-olds (n = 34), 8- to 10-year-olds (n = 34), 10- to 12-year-olds (n = 34) and adults (n = 20). Participants reported the coherent motion direction while high-density EEG was recorded. Using a data-driven approach, we identified two stimulus-locked EEG components with distinct topographies: an early component with an occipital topography likely reflecting sensory encoding and a later, sustained positive component over centro-parietal electrodes that we attribute to decision-related processes. The component waveforms showed clear age-related differences. In the early, occipital component, all groups showed a negativity peaking at ˜300 ms, like the previously reported coherent-motion N2. However, the children, unlike adults, showed an additional positive peak at ˜200 ms, suggesting differential stimulus encoding. The later positivity in the centro-parietal component rose more steeply for adults than for the youngest children, likely reflecting age-related speeding of decision-making. We conclude that children's protracted development of coherent motion sensitivity is associated with maturation of both early sensory and later decision-related processes.

Videos look faster as children grow up: Sense of speed and impulsivity throughout primary school

Previous research has documented systematic biases when adult observers judge the original speed of real-life video clips. What does the unfolding of events in videos-an increasingly pervasive "substitute reality"-look like as children grow up? The current study investigated the sense of speed during childhood and the relation with a number of performance and personality indexes. A group of 142 children aged 6-10 years adjusted the speed of video clips representing various scenes until reaching the apparent right speed. We found a tendency to underestimate speed; on average, videos played at their original speed were considered to be too slow. This tendency was larger in younger children and decreased with age (-3.16%/year). Uncertainty in judging video speed also decreased over the same age period (-10.79%/year). Children then performed a simple visuomotor task requiring response control, which revealed high accuracy and, in older children, faster responses. Children were also assessed for impulsivity/inattention and visuomotor habits through parents' questionnaires. When all variables were considered together, age and video game playing stood out as the only significant predictors of speed biases, both associated with an increase in apparent video speed. Thus, this study provides evidence of a change in the sense of speed during the primary school period, possibly involving the progressive overriding of a slow motion prior and/or the protracted calibration of perceptual mechanisms for speed constancy. The sense of speed, however, did not seem to be influenced by impulsivity traits in the population considered.

Development of Symbol Discrimination Speed in Children With Normal Vision

Purpose

Many visually guided tasks require rapid perception of visual details, but how fast children can discern foveal stimuli and how this ability improves with age are still unknown. To fill this gap, we tested normally sighted children between 5 and 12 years of age with a combined symbol-discrimination reaction-time test.

Methods

Children (n = 94) had to indicate, as fast and accurately as possible, the orientation of a Landolt C symbol (90 trials). Task difficulty was manipulated by varying symbol size (-0.43 to 1.09 logMAR at 5 m). The resulting reaction times were analyzed with a drift-diffusion model. Reaction times on a visual and auditory detection task were measured to assess the contribution of other factors, such as delays in stimulus detection and executing the motor response.

Results

Detection and discrimination were significantly faster in older children. Five-year-olds needed ∼440 ms for visual detection and ∼980 ms for discrimination of the largest symbols while 12-year-olds needed only ∼250 ms and ∼500 ms for this. The extra time needed for discrimination compared with detection decreased with age. The decrease in reaction time with increasing optotype size was also age-dependent and indicated an increase in sensitivity with age. Despite the time pressure, acuity thresholds were normal (within the EN ISO-8597 standard).

Conclusions

Our data revealed substantial developmental improvements in visual discrimination speed, which suggests that an important optimization takes place in the developing visual system of 5- to 12-year-old children. Since the speed-acuity test allows for quick and reliable assessment of visual recognition acuity and speed, it may be useful in clinical testing too.

Psychophysics with children: Investigating the effects of attentional lapses on threshold estimates

When assessing the perceptual abilities of children, researchers tend to use psychophysical techniques designed for use with adults. However, children's poorer attentiveness might bias the threshold estimates obtained by these methods. Here, we obtained speed discrimination threshold estimates in 6- to 7-year-old children in UK Key Stage 1 (KS1), 7- to 9-year-old children in Key Stage 2 (KS2), and adults using three psychophysical procedures: QUEST, a 1-up 2-down Levitt staircase, and Method of Constant Stimuli (MCS). We estimated inattentiveness using responses to "easy" catch trials. As expected, children had higher threshold estimates and made more errors on catch trials than adults. Lower threshold estimates were obtained from psychometric functions fit to the data in the QUEST condition than the MCS and Levitt staircases, and the threshold estimates obtained when fitting a psychometric function to the QUEST data were also lower than when using the QUEST mode. This suggests that threshold estimates cannot be compared directly across methods. Differences between the procedures did not vary significantly with age group. Simulations indicated that inattentiveness biased threshold estimates particularly when threshold estimates were computed as the QUEST mode or the average of staircase reversals. In contrast, thresholds estimated by post-hoc psychometric function fitting were less biased by attentional lapses. Our results suggest that some psychophysical methods are more robust to attentiveness, which has important implications for assessing the perception of children and clinical groups.

Neural Correlates of Speed-Tuned Motion Perception in Healthy Adults

It has been suggested that slow and medium-to-fast speeds of motion may be processed by at least partially separate mechanisms. The purpose of this study was to establish the cortical areas activated during motion-defined form and global motion tasks as a function of speed, using functional magnetic resonance imaging. Participants performed discrimination tasks with random dot stimuli at high coherence, at coherence near their own thresholds, and for random motion. Stimuli were moving at 0.1 or 5 deg/s. In the motion-defined form task, lateral occipital complex, V5/MT+ and intraparietal sulcus showed greater activation by high or near-threshold coherence than by random motion stimuli; V5/MT+ and intraparietal sulcus demonstrated greater activation for 5 than 0.1 deg/s dot motion. In the global motion task, only high coherence stimuli elicited significant activation over random motion; this activation was primarily in nonclassical motion areas. V5/MT+ was active for all motion conditions and showed similar activation for coherent and random motion. No regions demonstrated speed-tuning effects for global motion. These results suggest that similar cortical systems are activated by slow- and medium-speed stimuli during these tasks in healthy adults.

Effect of spatial and temporal stimulus parameters on the maturation of global motion perception

There are discrepancies with respect to the age at which adult-like performance is reached on tasks assessing global motion perception. This is in part because performance in children depends on stimulus parameters. We recently showed that five-year-olds demonstrated adult-like performance over a range of speeds when the speed ratio was comprised of longer spatial and temporal displacements; but displayed immature performance when the speed ratio was comprised of shorter displacements. The goal of the current study was to assess the effect of these global motion stimulus parameters across a broader age range in order to estimate the age at which mature performance is reached. Motion coherence thresholds were assessed in 182 children and adults aged 7-30years. Dot displacement (Δx) was 1, 5, or 30min of arc; frame duration (Δt) was 17 or 50ms. This created a total of six conditions. Consistent with our previous results, coherence thresholds in the youngest children assessed were adult-like at the two conditions with the largest Δx. Maturity was reached around age 12 for the medium Δx, and by age 16 for the smallest Δx. Performance did not appear to be affected by Δt. This late maturation may reflect a long developmental period for cortical networks underlying global motion perception. These findings resolve many of the discrepancies across previous studies, and should be considered when using global motion tasks to assess children with atypical development.

Genotype- and sex-dependent effects of altered Cntnap2 expression on the function of visual cortical areas

Background

Autism spectrum disorder (ASD) is a heritable, heterogeneous neurodevelopmental disorder that is four times more likely to affect males than females. Despite this overt sex bias, it is unclear how genetic mutations associated with ASD alter cortical circuitry to produce the behavioral phenotypes by which ASD is diagnosed. Contactin-associated protein-like 2 (CNTNAP2) is an ASD-associated gene, and while Cntnap2 knockout (KO) mice recapitulate many of the features of ASD, the effect on cortical circuitry is poorly understood. Moreover, although heterozygous (Het) mice are the more relevant genotype for ASD-linked CNTNAP2 mutations in humans, to our knowledge, no effects in Het mice have been previously reported.

Methods

Intrinsic signal optical imaging was used to measure functional visual responses in primary and higher visual cortical areas in male and female Cntnap2 KO, Het, and wild-type (WT) mice. Main effect of genotype was assessed with one-way ANOVA. Visual responses were also measured in P17–18 and P30–32 KO and WT mice. Main effects of age and genotype were assessed using two-way ANOVA.

Results

Visually evoked activity in dorsal stream associated higher visual areas in both KO and Het adult males was decreased relative to WT adult males. This decrease was not observed in adult females. Additionally, no significant difference was observed between WT and KO males at P17–18 with differences beginning to emerge at P30–32.

Conclusions

The functional responses of cortical circuitry in male mice are more strongly affected by Cntnap2 mutations than females, an effect present even in Hets. The observed differences in males emerge with development beginning at P30–32. These results reveal genotype- and sex-dependent effects of altered Cntnap2 expression and can shed light on the sex-dependent incidence of ASD.

Electronic supplementary material

The online version of this article (doi:10.1186/s11689-016-9182-5) contains supplementary material, which is available to authorized users.

Global motion perception in children with amblyopia as a function of spatial and temporal stimulus parameters

Global motion sensitivity in typically developing children depends on the spatial (Δx) and temporal (Δt) displacement parameters of the motion stimulus. Specifically, sensitivity for small Δx values matures at a later age, suggesting it may be the most vulnerable to damage by amblyopia. To explore this possibility, we compared motion coherence thresholds of children with amblyopia (7-14years old) to age-matched controls. Three Δx values were used with two Δt values, yielding six conditions covering a range of speeds (0.3-30deg/s). We predicted children with amblyopia would show normal coherence thresholds for the same parameters on which 5-year-olds previously demonstrated mature performance, and elevated coherence thresholds for parameters on which 5-year-olds demonstrated immaturities. Consistent with this, we found that children with amblyopia showed deficits with amblyopic eye viewing compared to controls for small and medium Δx values, regardless of Δt value. The fellow eye showed similar results at the smaller Δt. These results confirm that global motion perception in children with amblyopia is particularly deficient at the finer spatial scales that typically mature later in development. An additional implication is that carefully designed stimuli that are adequately sensitive must be used to assess global motion function in developmental disorders. Stimulus parameters for which performance matures early in life may not reveal global motion perception deficits.

Children's Brain Responses to Optic Flow Vary by Pattern Type and Motion Speed

Structured patterns of global visual motion called optic flow provide crucial information about an observer's speed and direction of self-motion and about the geometry of the environment. Brain and behavioral responses to optic flow undergo considerable postnatal maturation, but relatively little brain imaging evidence describes the time course of development in motion processing systems in early to middle childhood, a time when psychophysical data suggest that there are changes in sensitivity. To fill this gap, electroencephalographic (EEG) responses were recorded in 4- to 8-year-old children who viewed three time-varying optic flow patterns (translation, rotation, and radial expansion/contraction) at three different speeds (2, 4, and 8 deg/s). Modulations of global motion coherence evoked coherent EEG responses at the first harmonic that differed by flow pattern and responses at the third harmonic and dot update rate that varied by speed. Pattern-related responses clustered over right lateral channels while speed-related responses clustered over midline channels. Both children and adults show widespread responses to modulations of motion coherence at the second harmonic that are not selective for pattern or speed. The results suggest that the developing brain segregates the processing of optic flow pattern from speed and that an adult-like pattern of neural responses to optic flow has begun to emerge by early to middle childhood.

Spatial and temporal aspects of visual backward masking in children and young adolescents

The development of visual functions is very diverse. Some visual functions mature within the first year of life, whereas maturation for other functions extends into adolescence. The reasons for these developmental differences are largely unknown. Here, we investigated spatiotemporal processing in children (7–9 years, n = 15), young adolescents (11–13 years, n = 26), and adults (18–33 years, n = 24) using the shine-through visual backward-masking paradigm. We found that children had significantly longer vernier durations than either young adolescents or adults. However, children’s spatial and temporal processing of complex masks was very similar to that of young adolescents and adults. We suggest that spatiotemporal processing related to visual backward masking is already fully developed at age 7, whereas the attentional processes related to target enhancement only mature in young adolescence.

Motion perception: a review of developmental changes and the role of early visual experience

Significant controversies have arisen over the developmental trajectory for the perception of global motion. Studies diverge on the age at which it becomes adult-like, with estimates ranging from as young as 3 years to as old as 16. In this article, we review these apparently conflicting results and suggest a potentially unifying hypothesis that may also account for the contradictory literature in neurodevelopmental disorders, such as Autism Spectrum Disorder (ASD). We also discuss the extent to which patterned visual input during this period is necessary for the later development of motion perception. We conclude by addressing recent studies directly comparing different types of motion integration, both in typical and atypical development, and suggest areas ripe for future research.

Reading and coherent motion perception in school age children

This study includes an evaluation, according to age, of the reading and global motion perception developmental trajectories of 2027 school age children in typical stages of development. Reading is assessed using the reading rate score test, for which all of the student participants, regardless of age, received the same passage of text of a medium difficulty reading level. The coherent motion perception threshold is determined according to the adaptive psychophysical protocol based on a four-alternative, forced-choice procedure. Three different dot velocities: 2, 5, and 8 deg/s were used for both assemblies of coherent or randomly moving dots. Reading rate score test results exhibit a wide dispersion across all age groups, so much so that the outlier data overlap, for both the 8 and 18-year-old student-participant age groups. Latvian children's reading fluency developmental trajectories reach maturation at 12-13 years of age. After the age of 13, reading rate scores increase slowly; however, the linear regression slope is different from zero and positive: F(1, 827) = 45.3; p < 0.0001. One hundred eighty-one student-participants having results below the 10th percentile were classified as weak readers in our study group. The reading fluency developmental trajectory of this particular group of student-participants does not exhibit any statistically significant saturation until the age of 18 years old. Coherent motion detection thresholds decrease with age and do not reach saturation. Tests with slower moving dots (2 deg/s) yield results that exhibit significant differences between strong and weak readers.

Development of radial optic flow pattern sensitivity at different speeds

The development of sensitivity to radial optic flow discrimination was investigated by measuring motion coherence thresholds (MCTs) in school-aged children at two speeds. A total of 119 child observers aged 6-16years and 24 young adult observers (23.66+/-2.74years) participated. In a 2AFC task observers identified the direction of motion of a 5° radial (expanding vs. contracting) optic flow pattern containing 100 dots with 75% Michelson contrast moving at 1.6°/s and 5.5°/s and. The direction of each dot was drawn from a Gaussian distribution whose standard deviation was either low (similar directions) or high (different directions). Adult observers also identified the direction of motion for translational (rightward vs. leftward) and rotational (clockwise vs. anticlockwise) patterns. Motion coherence thresholds to radial optic flow improved gradually with age (linear regression, p<0.05), with different rates of development at the two speeds. Even at 16years MCTs were higher than that for adults (independent t-tests, p<0.05). Both children and adults had higher sensitivity at 5.5°/s compared to 1.6°/s (paired t-tests, p<0.05). Sensitivity to radial optic flow is still immature at 16years of age, indicating late maturation of higher cortical areas. Differences in sensitivity and rate of development of radial optic flow at the different speeds, suggest that different motion processing mechanisms are involved in processing slow and fast speeds.

Averaging, not internal noise, limits the development of coherent motion processing

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Motion processing abilities develop gradually through childhood.

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This lengthy development could be due to local noise and/or poor averaging.

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5–11-year-olds and adults performed equivalent noise and motion coherence tasks.

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Through childhood, internal noise reduces and averaging increases.

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Yet, only improved averaging explains developments in motion coherence sensitivity.

The development of motion processing is a critical part of visual development, allowing children to interact with moving objects and navigate within a dynamic environment. However, global motion processing, which requires pooling motion information across space, develops late, reaching adult-like levels only by mid-to-late childhood. The reasons underlying this protracted development are not yet fully understood. In this study, we sought to determine whether the development of motion coherence sensitivity is limited by internal noise (i.e., imprecision in estimating the directions of individual elements) and/or global pooling across local estimates. To this end, we presented equivalent noise direction discrimination tasks and motion coherence tasks at both slow (1.5°/s) and fast (6°/s) speeds to children aged 5, 7, 9 and 11 years, and adults. We show that, as children get older, their levels of internal noise reduce, and they are able to average across more local motion estimates. Regression analyses indicated, however, that age-related improvements in coherent motion perception are driven solely by improvements in averaging and not by reductions in internal noise. Our results suggest that the development of coherent motion sensitivity is primarily limited by developmental changes within brain regions involved in integrating motion signals (e.g., MT/V5).

How children and adults learn to intercept moving gaps

We used an immersive virtual environment to examine how children and adults learn to intercept moving gaps and whether children and adults benefit from variability of practice. Children (10- and 12-year-olds) and adults attempted to bicycle between two moving vehicle-size blocks without stopping. In Experiment 1, block motions were timed such that if participants maintained a constant speed, they would intercept the gap between the blocks. By the last set of intersections, adults learned to maintain a constant speed throughout the approach to the intersection, 12-year-olds exhibited less variability in time-to-spare when they intercepted the blocks, and 10-year-olds exhibited no significant change across intersection sets. In Experiment 2, block motions during the first eight intersections were timed such that participants needed to either speed up or slow down on all intersections or needed to speed up on half and slow down on half of the intersections. On the last four intersections, all age groups encountered a novel block timing in which no adjustment in speed was necessary to intercept the blocks. The adults performed well regardless of whether they experienced consistent or variable block timings. The 10-year-olds in the variable condition performed better on slow-down trials than their peers in the slow-down condition but performed worse on speed-up trials than their peers in the speed-up condition. Discussion focuses on possible developmental changes in reliance on perceptually available and remembered information in complex perception-action tasks.

Development of sampling efficiency and internal noise in motion detection and discrimination in school-aged children

The aim of this study was to use an equivalent noise paradigm to investigate the development and maturation of motion perception, and how the underlying limitations of sampling efficiency and internal noise effect motion detection and direction discrimination in school-aged children (5-14 years) and adults. Contrast energy thresholds of a 2c/deg sinusoidal grating drifting at 1.0 or 6.0 Hz were measured as a function of added dynamic noise in three tasks: detection of a drifting grating; detection of the sum of two oppositely drifting gratings and direction discrimination of oppositely drifting gratings. Compared to the ideal observer, in both children and adults, the performance for all tasks was limited by reduced sampling efficiency and internal noise. However, the thresholds for discrimination of motion direction and detection of moving gratings show very different developmental profiles. Motion direction discrimination continues to improve after the age of 14 years due to an increase in sampling efficiency that differs with speed. Motion detection and summation were already mature at the age of 5 years, and internal noise was the same for all tasks. These findings were confirmed in a 1-year follow-up study on a group of children from the initial study. The results support suggestions that the detection of a moving pattern and discriminating motion direction are processed by different systems that may develop at different rates.

The development of global motion discrimination in school aged children

Global motion perception matures during childhood and involves the detection of local directional signals that are integrated across space. We examine the maturation of local directional selectivity and global motion integration with an equivalent noise paradigm applied to direction discrimination. One hundred and three observers (6-17 years) identified the global direction of motion in a 2AFC task. The 8° central stimuli consisted of 100 dots of 10% Michelson contrast moving 2.8°/s or 9.8°/s. Local directional selectivity and global sampling efficiency were estimated from direction discrimination thresholds as a function of external directional noise, speed, and age. Direction discrimination thresholds improved gradually until the age of 14 years (linear regression, p < 0.05) for both speeds. This improvement was associated with a gradual increase in sampling efficiency (linear regression, p < 0.05), with no significant change in internal noise. Direction sensitivity was lower for dots moving at 2.8°/s than at 9.8°/s for all ages (paired t test, p < 0.05) and is mainly due to lower sampling efficiency. Global motion perception improves gradually during development and matures by age 14. There was no change in internal noise after the age of 6, suggesting that local direction selectivity is mature by that age. The improvement in global motion perception is underpinned by a steady increase in the efficiency with which direction signals are pooled, suggesting that global motion pooling processes mature for longer and later than local motion processing.

Visual motion processing and visual sensorimotor control in autism

Impairments in visual motion perception and use of visual motion information to guide behavior have been reported in autism, but the brain alterations underlying these abnormalities are not well characterized. We performed functional magnetic resonance imaging (fMRI) studies to investigate neural correlates of impairments related to visual motion processing. Sixteen high-functioning individuals with autism and 14 age and IQ-matched typically developing individuals completed two fMRI tasks using passive viewing to examine bottom-up responses to visual motion and visual pursuit tracking to assess top-down modulation of visual motion processing during sensorimotor control. The autism group showed greater activation and faster hemodynamic decay in V5 during the passive viewing task and reduced frontal and V5 activation during visual pursuit. The observations of increased V5 activation and its faster decay during passive viewing suggest alterations in local V5 circuitries that may be associated with reduced GABAergic tone and inhibitory modulation. Reduced frontal and V5 activation during active pursuit suggest reduced top-down modulation of sensory processing. These results suggest that both local intrinsic abnormalities in V5 and more widely distributed network level abnormalities are associated with visual motion processing in autism.

The maturation of global motion perception depends on the spatial and temporal offsets of the stimulus

The typical development of motion perception is commonly assessed with tests of global motion integration using random dot kinematograms. There are discrepancies, however, with respect to when typically-developing children reach adult-like performance on this task, ranging from as early as 3 years to as late as 12 years. To address these discrepancies, the current study measured the effect of frame duration (Δt) and signal dot spatial offset (Δx) on motion coherence thresholds in adults and children. Two Δt values were used in combination with seven Δx values, for a range of speeds (0.3-38 deg/s). Developmental comparisons showed that for the longer Δt, children performed as well as adults for larger Δx, and were immature for smaller Δx. When parameters were expressed as speed, there was a range of intermediate speeds (4-12 deg/s) for which maturity was dependent on the values of Δx and Δt tested. These results resolve previous discrepancies by showing that motion sensitivity to a given speed may be mature, or not, depending on the underlying spatial and temporal properties of the motion stimulus.

Processing slow and fast motion in children with autism spectrum conditions

Consistent with the dorsal stream hypothesis, difficulties processing dynamic information have previously been reported in individuals with autism spectrum conditions (ASC). However, no research has systematically compared motion processing abilities for slow and fast speeds. Here, we measured speed discrimination thresholds and motion coherence thresholds in slow (1.5 deg/sec) and fast (6 deg/sec) speed conditions in children with an ASC aged 7 to 14 years, and age- and ability-matched typically developing children. Unexpectedly, children with ASC were as sensitive as typically developing children to differences in speed at both slow and fast reference speeds. Yet, elevated motion coherence thresholds were found in children with ASC, but in the slow stimulus speed condition only. Rather than having pervasive difficulties in motion processing, as predicted by the dorsal stream hypothesis, these results suggest that children with ASC have a selective difficulty in extracting coherent motion information specifically at slow speeds. Understanding the effects of stimulus parameters such as stimulus speed will be important for resolving discrepancies between previous studies examining motion coherence thresholds in ASC and also for refining theoretical models of altered autistic perception.