David R. Simmons

Vision in autism spectrum disorders

Autism spectrum disorders (ASDs) are developmental disorders which are thought primarily to affect social functioning. However, there is now a growing body of evidence that unusual sensory processing is at least a concomitant and possibly the cause of many of the behavioural signs and symptoms of ASD. A comprehensive and critical review of the phenomenological, empirical, neuroscientific and theoretical literature pertaining to visual processing in ASD is presented, along with a brief justification of a new theory which may help to explain some of the data, and link it with other current hypotheses about the genetic and neural aetiologies of this enigmatic condition.

Contrast Thresholds for Stereoscopic Depth Identification with Isoluminant and Isochromatic Stimuli

Contrast thresholds for stereoscopic depth identification (crossed or uncrossed) were measured as a function of disparity using isoluminant (red-green) and isochromatic (yellow-black) 0.5 c/deg Gabor patches. For the purposes of comparison stimulus contrasts were scaled by their respective detection thresholds. The detection thresholds employed were computed from the monocular detection thresholds of the stereo half-images, based on the assumption that simultaneous detection of these half-images in each eye was a sufficient condition for stereopsis. It was found that the disparity tuning of both chromatic and luminance mechanisms was similar, with a performance peak for a binocular phase disparity of 50-120 deg. However, more contrast was required, relative to detection threshold, for the chromatic patterns to evoke a sensation of stereoscopic depth. These results suggest that stereopsis in the absence of luminance cues is supported by a less-contrast-sensitive analogue of the system that supports stereopsis in the presence of luminance cues. The results are also consistent with there being a lower density of disparity-selective mechanisms in the chromatic pathway. The implications of these data for previous studies of stereopsis at isoluminance is discussed.

Do distinct atypical cortical networks process biological motion information in adults with autism spectrum disorders.

Whether people with Autism Spectrum Disorders (ASDs) have a specific deficit when processing biological motion has been a topic of much debate. We used psychophysical methods to determine individual behavioural thresholds in a point-light direction discrimination paradigm for a small but carefully matched groups of adults (N=10 per group) with and without ASDs. These thresholds were used to derive individual stimulus levels in an identical fMRI task, with the purpose of equalising task performance across all participants whilst inside the scanner. The results of this investigation show that despite comparable behavioural performance both inside and outside the scanner, the group with ASDs shows a different pattern of BOLD activation from the TD group in response to the same stimulus levels. Furthermore, connectivity analysis suggests that the main differences between the groups are that the TD group utilise a unitary network with information passing from temporal to parietal regions, whilst the ASD group utilise two distinct networks; one utilising motion sensitive areas and another utilising form selective areas. Furthermore, a temporal-parietal link that is present in the TD group is missing in the ASD group. We tentatively propose that these differences may occur due to early dysfunctional connectivity in the brains of people with ASDs, which to some extent is compensated for by rewiring in high functioning adults.

On the binocular summation of chromatic contrast

The binocular summation of chromatic contrast was investigated under a variety of stimulus conditions. Binocular and monocular contrast detection thresholds were measured using 0.5 cpd Gabor patches. It was found that, using stimuli which contained combinations of chromatic and luminance contrast, binocular detection could take place independently in luminance-contrast- and chromatic-contrast-sensitive mechanisms. It was also found that, with chromatic stimuli, levels of binocular summation were above those expected from probability summation between the eyes, and thus showed evidence for binocular neural summation within chromatic detection mechanisms. The implications of these results for (a) the binocularity of chromatic detection mechanisms, and (b) the suggested link between stereopsis and binocular neural summation, are discussed.

On the independence of chromatic and achromatic stereopsis mechanisms

The extent to which the processing of stereoscopic depth information can take place separately in colour-contrast-sensitive and luminance-contrast-sensitive mechanisms has been investigated. Contrast thresholds for stereoscopic depth identification (front/back) were measured using 0.5 c/deg Gabor patches. The stimuli possessed different amounts of colour and luminance contrast ranging from isoluminance (red/green) to isochrominance (yellow/black) through intermediate values. Two models for combining chromatic and achromatic stereopsis information were tested. The first (single-pathway) model assumed colour and luminance contrast summation within a single luminance-contrast-sensitive mechanism before stereoscopic judgement. The second (dual-pathway) model assumed probability summation between independent chromatic and achromatic stereopsis mechanisms. The latter model provided the better fit to the data. In providing evidence in favour of an independent chromatic stereopsis mechanism, it was shown that luminance artifacts were unlikely to be the cause of maintained stereopsis at isoluminance. The possible neural substrates of chromatic stereopsis are discussed.

Stereoacuity and colour contrast

We have measured the contrast dependence of stereoacuity using both horizontally and vertically oriented, isoluminant (red-green) and isochromatic (yellow-black), 0.5 c/deg Gabor patches. For comparison, contrasts were computed in multiples of detection threshold, where detection threshold was defined as the contrast required for the stimulus to be simultaneously detectable in each eye. Disparity thresholds (1/stereoacuity) for vertical chromatic Gabors were higher than those for vertical luminance Gabors by a factor of between 4 and 9 depending on contrast, and declined less steeply with contrast. Disparity thresholds for horizontal chromatic Gabors were very high (130-210 min arc) compared with horizontal luminance Gabors (by a factor of between 9 and 17) and were only measurable at contrasts above 10 times simultaneous monocular detection threshold. These results support the view that chromatic stereoscopic processing is less precise than luminance stereoscopic processing, and that there is a special deficit in the processing of disparity with horizontally oriented chromatic stimuli. The implications of these results for the role of colour vision in stereopsis are discussed.

The Binocular Combination of Chromatic Contrast

How is chromatic contrast combined binocularly? One index of binocularity is the binocular contrast summation ratio (BCSR), which is the improvement in contrast sensitivity with binocular rather than monocular presentation. Simmons and Kingdom (1998, Vision Research 38 1063–1071) noted that BCSRs with some red-green isoluminant stimuli were suggestive of full linear summation. This suggestion was investigated further in four subjects by measuring binocular and monocular contrast thresholds for the detection of 0.5 cycle deg−1 isoluminant (red-green) and isochromatic (yellow-black) Gabor patches. These Gabor patches had either vertically or horizontally oriented carrier gratings and were either dichoptically in phase (same coloured bars in binocular correspondence) or in dichoptic anti-phase (opposite coloured bars in binocular correspondence). Full linear summation would be indicated by BCSRs of 2 for the in-phase and close to 0 for the anti-phase conditions. Mean BCSRs at isoluminance were 1.93 and 0.90, respectively, for the in-phase and anti-phase stimuli with horizontal carriers, the former being consistent with full linear summation, but the latter not. Despite these results, BCSRs obtained with isoluminant and isochromatic stimuli under similar conditions were not statistically distinguishable from each other, although there was a tendency for summation at isoluminance with in-phase stimuli to be higher and anti-phase stimuli to be lower. These data fall short of demonstrating full linear summation of chromatic contrast between the eyes under all presentation conditions, but they do indicate that there are strong binocular interactions at red-green isoluminance, which are similar to, and possibly even stronger than, those obtained with luminance stimuli.

Three-dimensional assessment of facial appearance following surgical repair of unilateral cleft lip and palate.

Background and Objective Objective assessment of postsurgical facial asymmetry can be difficult, but three-dimensional (3D) imaging techniques have made this possible. The objective of this study was to assess residual asymmetry in surgically repaired unilateral cleft lip (UCL) and unilateral cleft lip and palate (UCLP) patients and to compare this with noncleft controls. Design Retrospective multicohort comparative study. Patients and Methods Fifty-one 10-year-old children with surgically managed UCLP and 44 children with UCL were compared with a control group of 68 ten-year-olds. The 3D facial models at rest and with maximum smile were created using a 3D imaging system. Asymmetry scores were produced using both anatomical landmarks and a novel method of facial curve analysis. Results Asymmetry for the whole face was significantly higher in both cleft groups compared with controls (P < .001). UCLP asymmetry was higher than UCL (P < .001). In cleft patients, the upper lip and nasal rim were the most asymmetric (P < .001 to .05). Control subjects also displayed a degree of facial asymmetry. Maximum smile did not significantly affect the symmetry of the whole face, but it increased asymmetry of the vermillion border and nasal rim in all three groups (P < .001). Conclusions Despite surgical intervention at an early age, asymmetry remains significant in cleft patients at 10 years of age. Three-dimensional imaging is a noninvasive objective assessment tool that identifies specific areas of the face responsible for asymmetry. Facial curve analysis describes the face more comprehensively and characterizes soft tissue contours.

A Review of Serious Games for Children with Autism Spectrum Disorders (ASDs)

This paper reviews 40 serious games designed for children with autism spectrum disorders (ASD) and these games/studies are classified into four categories; technology platform, computer graphics, gaming aspect and user interaction. Moreover, the paper discusses serious games designed for the improvement of communication skills and social behavior, social conversation, imaginative skills, sensory integration and learning accounts in ASD children. The children usually interact with these games by ordinary IO (input/output) e.g. keyboard and mouse or touchscreen tools. Previous researches show the effectiveness of playing serious games on mobiles or tablet devices in helping ASD children to express their feelings and improve the level of engagement with others. However, there are limitations in designing games for helping autistic children with sensory processing disorder (SPD), improving imaginative play, and teaching first aid. Further, there is not much research that addresses repetitive behavior in ASD children.

3D assessment of lip scarring and residual dysmorphology following surgical repair of cleft lip and palate: a preliminary study.

Objective To evaluate lip scarring and the three-dimensional (3D) lip morphology following primary reconstruction in children with unilateral cleft lip and palate (UCLP) relative to contemporaneous noncleft data. Design Retrospective, cross-sectional, controlled study. Setting Glasgow Dental Hospital and School, University of Glasgow, U.K. Patients and participants Three groups of 10-year-old children: 51 with UCLP, 43 UCL (unilateral cleft lip), and 68 controls. Methods Three-dimensional images of the face were recorded using stereo cameras on a two-pod capture station, and 3D coordinates of anthropometric landmarks were extracted from the facial images. A novel method was applied to quantify residual scarring and the associated lip dysmorphologies. The relationships among outcome measures were investigated. Results Residual lip dysmorphologies were more pronounced in UCLP cases. The width of the Cupids bow was increased due to lateral displacement of the Christa philteri left (cphL) in both UCL and UCLP patients. In the upper part of the lip, the nostril base was significantly wider in UCLP cases when compared with UCL cases and controls. Scar redness was more pronounced in UCL than in UCLP cases. No relationship could be identified between lip scarring and other measurements of lip dysmorphology. Conclusions Stereophotogrammetry, together with associated image analysis, allow early detection of residual dysmorphology following cleft repair.