Differential habituation to repeated sounds in infants at high risk for autism

It has been suggested that poor habituation to stimuli might explain atypical sensory behaviours in autism, i.e. over-responsiveness to some stimuli and under-sensitivity to other. We investigated habituation to repeated sounds using an oddball paradigm in 9 month-old infants with an older sibling with autism and hence at high risk for developing autism. Auditory evoked responses to repeated sounds in control infants (at low risk of developing autism) decreased over time, demonstrating habituation, and their responses to deviant sounds were larger than responses to standard sounds, indicating discrimination. In contrast, neural responses in infants at high risk showed no habituation, and reduced sensitivity to changes in frequency. Reduced sensory habituation may be present at a younger age than the emergence of autistic behaviour in some individuals, and we propose that this could play a role in the sensory atypicalities observed in autism

Atypical audiovisual speech integration in infants at risk for autism

The language difficulties often seen in individuals with autism might stem from an inability to integrate audiovisual information, a skill important for language development. We investigated whether 9-month-old siblings of older children with autism, who are at an increased risk of developing autism, are able to integrate audiovisual speech cues. We used an eye-tracker to record where infants looked when shown a screen displaying two faces of the same model, where one face is articulating/ba/and the other/ga/, with one face congruent with the syllable sound being presented simultaneously, the other face incongruent. This method was successful in showing that infants at low risk can integrate audiovisual speech: they looked for the same amount of time at the mouths in both the fusible visual/ga/− audio/ba/and the congruent visual/ba/− audio/ba/displays, indicating that the auditory and visual streams fuse into a McGurk-type of syllabic percept in the incongruent condition. It also showed that low-risk infants could perceive a mismatch between auditory and visual cues: they looked longer at the mouth in the mismatched, non-fusible visual/ba/− audio/ga/display compared with the congruent visual/ga/− audio/ga/display, demonstrating that they perceive an uncommon, and therefore interesting, speech-like percept when looking at the incongruent mouth (repeated ANOVA: displays x fusion/mismatch conditions interaction: F(1,16) = 17.153, p = 0.001). The looking behaviour of high-risk infants did not differ according to the type of display, suggesting difficulties in matching auditory and visual information (repeated ANOVA, displays x conditions interaction: F(1,25) = 0.09, p = 0.767), in contrast to low-risk infants (repeated ANOVA: displays x conditions x low/high-risk groups interaction: F(1,41) = 4.466, p = 0.041). In some cases this reduced ability might lead to the poor communication skills characteristic of autism

Human Decision Making Based on Variations in Internal Noise: An EEG Study

Perceptual decision making is prone to errors, especially near threshold. Physiological, behavioural and modeling studies suggest this is due to the intrinsic or ‘internal’ noise in neural systems, which derives from a mixture of bottom-up and top-down sources. We show here that internal noise can form the basis of perceptual decision making when the external signal lacks the required information for the decision. We recorded electroencephalographic (EEG) activity in listeners attempting to discriminate between identical tones. Since the acoustic signal was constant, bottom-up and top-down influences were under experimental control. We found that early cortical responses to the identical stimuli varied in global field power and topography according to the perceptual decision made, and activity preceding stimulus presentation could predict both later activity and behavioural decision. Our results suggest that activity variations induced by internal noise of both sensory and cognitive origin are sufficient to drive discrimination judgments

Differential habituation to repeated sounds in infants at high risk for autism

It has been suggested that poor habituation to stimuli might explain atypical sensory behaviours in autism. We investigated habituation to repeated sounds using an oddball paradigm in 9-month-old infants with an older sibling with autism and hence at high risk for developing autism. Auditory-evoked responses to repeated sounds in control infants (at low risk of developing autism) decreased over time, demonstrating habituation, and their responses to deviant sounds were larger than responses to standard sounds, indicating discrimination. In contrast, neural responses in infants at high risk showed less habituation and a reduced sensitivity to changes in frequency. Reduced sensory habituation may be present at a younger age than the emergence of autistic behaviour in some individuals, and we propose that this could play a role in the over responsiveness to some stimuli and undersensitivity to others observed in autism

Comparison of ‘chosen’ and ‘non-chosen’ responses: Global field potential (GFP).

<div><p>(A) Single-electrode traces (33 channels) for chosen (magenta) and non-chosen (blue) responses, grand averaged across presentation intervals and subjects. Grey patches demarcate times during which there was a significant difference between GFP for the chosen and non-chosen stimuli (see B and C). The pink patches demarcate areas of significant topographic dissimilarity (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0068928#pone-0068928-g004" target="_blank">Figure 4</a>).</p> <p>(B) GFP for responses to stimuli ‘chosen’ as different (magenta) and ‘non-chosen’ (blue). These measures are independent of topography differences. Grey patches are as above.</p> <p>(C) Statistical analysis of the GFP: A permutation test was run to control for family-wise error rate (FWER) associated with multiple comparisons across the ERP time-course. The t-statistic associated with the difference between chosen and non-chosen GFP is in black, and criterion t-value controlling for the FWER is marked by the dashed red line. The grey areas demarcate time points at which the t-statistic exceeded the criterion value.</p> <p>(D) Topographic plots showing the difference between chosen and non-chosen activity at various time-points with significant GFP differences. The color bar indicates differences in microvolts.</p></div

Differences between chosen and non-chosen responses in the final stimulus interval.

<div><p>(A) ERP waveforms for chosen (magenta) and non-chosen (blue) stimuli in interval 3. Each trace represents an electrode channel. The colored underlays match the statistical maps in B and C.</p> <p>(B) Global field potential (GFP) for chosen and non-chosen stimuli in interval 3. The grey patches demarcate regions where the contrast exceeds the criterion t-value calculated using the permutation test to control for multiple comparisons.</p> <p>(C) Topographic dissimilarity for the chosen vs. non-chosen contrast in interval 3. The pink patch demarcates consecutive significance over ≥10 ms.</p> <p>(D) Topographic plots of chosen (top) and non-chosen (bottom) average activity at selected time-points. The color bar shows potential in microvolts.</p></div

Grand average event-related potentials (ERPs).

<div><p>(A) ERPs associated with chosen (magenta) and non-chosen (blue) stimuli, averaged across intervals and listeners, shown on selected electrodes plotted to approximate topography.</p><p>(B) Enlarged plots for ERPs to chosen and non-chosen stimuli on a fronto-central electrode (Fz; top) and a lateral electrode (TP10; bottom) show the polarity reversal typically associated with generators in the auditory cortex on the superior temporal plane.</p><p>(C) Marginal means associated with the absolute N1-P2 mean amplitude differences for chosen (magenta) and non-chosen (blue) stimuli at fronto-central and lateral sites. Error-bars denote the within-subject confidence intervals for the chosen – non-chosen difference after removing inter-subject variability (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0068928#B58" target="_blank">58</a>).</p><p>(D) ERPs for interval 1 (purple), 2 (red) and 3 (orange), averaged across chosen and non-chosen stimuli and listeners.</p><p>(E) Enlarged plot for the ERPs in each interval on the midline central electrode (Cz).</p></div

Experimental design and main factors in the statistical model.

<div><p>(A) Testing was divided into eight blocks of 100 trials with brief pauses between runs and a longer, 10-minute rest break between block 4 and 5. Each trial consisted of three stimulus intervals, each containing an identical 1-kHz tone. The tones were 100 ms long, separated by a 506 ms silent inter-stimulus interval (plus jitter; see Methods section) to a total trial-duration of approximately 1320 ms.</p><p>The statistical model incorporated the following factors:</p> <p>(B) Activity produced by stimuli ‘chosen’ as different (magenta), indicated by a button press, was compared to that produced by ‘non-chosen’ stimuli (blue).</p> <p>(C) Activity was compared for interval 1 (purple), 2 (red) and 3 (orange) for each trial.</p> <p>The same color scheme is used for the traces in subsequent figures.</p></div

Topographic dissimilarity associated with chosen and non-chosen stimuli.

<div><p>(A) The black traces show the topographic dissimilarity across time with random allocation of chosen and non-chosen epochs (5000 iterations). The measured dissimilarity for our original data set is shown in red. The pink patch demarcates a time region of statistical significance ≥10 ms.</p> <p>(B) Statistical map showing the likelihood of the measured dissimilarity being greater than 95% of the simulated data, as a non-parametric test of significance. The green line marks p = 0.05.</p> <p>(C) Chosen (top), non-chosen (middle) and difference (bottom) topographies associated with the time regions showing a statistically-significant contrast.</p></div

Looking time of infants at low versus high risk for autism in a McGurk paradigm.

<p>Low-risk infants looked as long at the incongruent mouth as at the congruent mouth in the fusion condition, demonstrating that they can integrate AV speech information, and they looked longer at the incongruent mouth than at the congruent mouth in the mismatch condition, indicating that they perceive incongruent, non-fusible AV speech information. In contrast, high-risk infants had the same looking behaviours in both the mismatch and fusion conditions, reflecting poor AV integration and detection of incongruence between AV information. Error bars are standard error of the means. *<i>p</i><0.05.</p