M79. COMPONENTS OF VISUAL SEARCH IN EARLY-ONSET SCHIZOPHRENIA, ADHD AND ASD: AN EYE TRACKING STUDY
Authors: Canu Daniela , Ioannou Chara , Müller Katarina , Martin Matthias , Bender Stephan , Biscaldi Monica , Fleischhaker Christian , Smyrnis Nikos , Klein Christoph 
Published: May 2020

Abstract

Background
Superior visual search is a replicated finding in the literature on Autism Spectrum Disorder (ASD). Conversely, results from the literature on Attention-Deficit/Hyperactivity Disorder (ADHD) are more mixed, with some studies showing typical performance and others pointing out less efficient serial search in ADHD. Finally, most studies on visual search in Schizophrenia highlighted deficits in focal attentional processing. However, similarities between attentional impairments in the three clinical groups have also been reported. The primary goal of our study is to determine the diagnostic specificity of search deficits. To our knowledge, the literature systematically comparing the visual search performance in patients with ADHD and Schizophrenia is limited to one study, while no study has so far included an ASD group in the comparison.

Methods
Four groups of young adults, namely 29 typically developing (TD; 19.8±1.6, 41% males), 26 with ASD (19.7±1.9, 96% males), 28 with ADHD (19.9±1.4, 54% males) and 21 with Early-Onset Schizophrenia (SCZ; 19.7±1.7, 71% males) were presented a visual search task in which they had to quickly detect a target item among several similar-to-target distractor items. Eye movements were recorded binocularly with the Eye Link 1000+ system. Participants were matched on age and full-scale IQ. The ocular-motor behaviour was analysed using Data Viewer 3.2 and SPSS 2.3.

Results
Initiation of search – latency of the first saccade on the search grid – was typical in all participants except those with SCZ, who had significant higher intra-subject variability (ISV) than both TD and ADHD, but no delay in initiating search. Within search, ASD manifested significantly reduced mean and ISV of total search duration – between the first saccade on the grid and the last fixation on target – and of the first part of search – between the first saccade on the grid and the first fixation on target – in comparison with all other groups, including TD. Conversely, SCZ and ASD were significantly more variable than TD and ADHD regarding the duration of first fixation on target, while also being, to a lesser extent, slower than ADHD, but not than TD. Additionally, SCZ needed a higher frequency of fixations on target than ASD, but not compared to ADHD or TD, before making a decision. In the post-search phase – between the onset of the last fixation on target and the button press on the keyboard – SCZ were the slowest and most variable group, followed by ASD and ADHD who differed?non-significantly? from controls. The overall search performance – between trial onset and button press – resulted in typical manual mean RT in ASD and ADHD while being atypically longer in SCZ, compared to all other groups. Compared to TD, ISV was at par in ADHD, lower in ASD, and higher in SCZ.

Discussion
Results suggest that the ability to extract individual targets is intact in ASD and ADHD. However, ASD only show a bias toward local information, as indicated by more variable first fixation duration, despite intact global processing. By contrast, lower search efficiency in SCZ might be explained by both (a) abnormal global processing due to impairment in the guidance mechanisms that affect the time until the first fixation on target, and (b) a deficit in central discrimination, with resulting difficulties in extracting critical features of the target.