Signal-to-noise ratios in the autism group were positively correlated with IQ scores (Figure 5, middle) and negatively correlated with autism symptom severity as assessed by the ADOS test (Figure 5, bottom) in all three experiments. However, only the correlation between signal-to-noise and IQ in the visual experiment was statistically significant. There was no evidence of signal-to-noise differences across subject groups in subcortical nuclei (Figure 6). We manually identified two subcortical ROIs—the lateral geniculate nucleus (LGN) and the medial geniculate nucleus (MGN)—using the average activation maps across all subjects in each group (Figure 1). Analyses of the responses in the two ROIs did not

reveal any significant differences between groups in any of the measures (Figures GDC-0941 concentration 6A–6C). Both subject groups exhibited robust motor responses when indicating letter repeats via a button press (Figure 7A). We used these responses to identify three motor ROIs (Figure S2): left primary motor cortex (Mot), right and left anterior intraparietal sulcus (aIPS), and

right and left ventral premotor cortex (vPM). Response FK228 amplitude, variability, and signal-to-noise were statistically indistinguishable across the two groups across all three ROIs (Figure 7). In this analysis, we combined trials across all three experiments because the task at fixation was identical. Individuals with autism were significantly slower and less accurate in detecting letter repeats than controls. This raised a concern

that the higher trial-by-trial sensory response variability reported in the autism group might be a consequence of the performance difference across groups. To address this issue, we excluded eight scans with the poorest performance below in the autism group and four scans with the best performance in the control group, so as to match mean accuracy and reaction times across groups (Figures 8A and 8B). Cortical response signal-to-noise ratios remained significantly smaller in the autism group (Figure 8C) even when behavioral performance was statistically indistinguishable across groups. The behavioral analyses also revealed that trial-by-trial variability in reaction times was larger in individuals with autism when comparing across all scans and when considering only the subset of scans for which mean accuracy and reaction times were matched across groups (Figure S6). We performed several control analyses to ensure that larger trial-by-trial fMRI variability in the autism group was not caused by more variable head motion, heart rate, respiration, or eye fixation during the experiments. The variability of all six head motion estimates, derived during 3D motion correction, was statistically indistinguishable across groups as was the mean frame-by-frame displacement (Figures S7A and S7B). Furthermore, we reanalyzed the fMRI responses after removing head motion parameters using orthogonal projection (Fox et al.