How Do Visual Search Abilities Compare Across Autism, ADHD, and Schizophrenia?

What you need to know

This study compared visual search abilities in autism, ADHD, schizophrenia, and typical development using eye tracking technology.
Schizophrenia showed the most impaired performance overall, followed by ADHD, while autism showed some strengths alongside weaknesses.
All three clinical groups showed similarities in their patterns of performance differences compared to typical development.
The findings support the idea of a continuum of neurodevelopmental impairment across these disorders.

Background and Methods

Autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), and schizophrenia are typically considered distinct conditions. However, research has found they share some genetic risk factors and brain differences. This has led to the idea that these disorders may exist on a continuum of neurodevelopmental impairment.

To explore this, the researchers compared performance on a visual search task across four groups of adolescents and young adults:

20 with schizophrenia
28 with ADHD
26 with ASD
29 typically developing controls

In the task, participants had to find a target item (a square with a gap on the top or bottom) among 15 distractor items (squares with gaps on the left or right sides). Their eye movements were recorded as they performed the search.

This allowed the researchers to break down the search process into different phases and analyze various aspects of performance, including:

How quickly participants responded overall
How long it took to start searching
How long they spent actually searching
How long it took to respond after finding the target
How variable their performance was from trial to trial
Characteristics of their eye movements, like fixation duration

Key Findings

Overall Performance

Schizophrenia showed the most impaired performance across multiple measures. They were slower to respond overall and showed more variability in their performance from trial to trial.

ADHD performance was often in between schizophrenia and controls. They showed some slowing and increased variability, but not to the same degree as schizophrenia.

ASD showed a mix of strengths and weaknesses. They were actually faster than controls in some aspects of search, but slower in others.

Search Initiation

Both schizophrenia and ASD groups were slower to start searching compared to controls. The researchers suggest this may reflect difficulties with “top-down” control of attention - the ability to purposefully direct attention based on task goals.

ADHD did not show this delay in starting to search.

Search Execution

The schizophrenia group spent more time actively searching compared to the other groups. This may indicate difficulties efficiently processing visual information or using working memory during search.

The ADHD group did not differ from controls in search time.

Interestingly, the ASD group was actually faster than the other groups in their search time. This aligns with previous research showing enhanced visual search abilities in autism in some contexts.

Response After Finding Target

Both schizophrenia and ASD groups took longer to respond after locating the target compared to controls. This may reflect difficulties with decision-making.

The ADHD group did not show this delay.

Eye Movement Characteristics

All three clinical groups showed longer fixation durations (time spent looking at individual items) compared to controls. This suggests they all had some difficulty quickly processing and identifying individual search items.

However, the ASD group made fewer eye movements overall and looked at fewer items compared to the other groups. This more restricted scanning pattern, combined with their faster search times, suggests they were able to more efficiently discriminate between targets and distractors.

Variability in Performance

Increased variability in performance from trial to trial was most pronounced in the schizophrenia group, who showed this across multiple measures.

The ADHD group showed increased variability in some measures, particularly at the start of search.

The ASD group showed a mix of increased and decreased variability depending on the specific measure.

Towards a Continuum of Impairment

While there were distinct patterns of performance for each clinical group, the researchers also found evidence supporting the idea of a continuum of impairment across the disorders:

The profiles of performance differences compared to controls were highly correlated between the clinical groups. This suggests the disorders show similar patterns of strengths and weaknesses, just to different degrees.
The overall level of impairment decreased from schizophrenia (most impaired) to ADHD to ASD (least impaired).
There were several areas of overlap in atypical performance shared by two or more of the clinical groups.

The authors argue this provides evidence for overlapping mechanisms of brain dysfunction across the disorders, despite their distinct symptoms. They suggest these disorders may exist on a spectrum of neurodevelopmental impairment, with schizophrenia representing the most severe end.

Conclusions

Visual search performance revealed both distinct and overlapping patterns of cognitive differences in schizophrenia, ADHD, and ASD compared to typical development.
The findings support the concept of a continuum of neurodevelopmental impairment across these disorders, with schizophrenia showing the most severe impairments.
Eye tracking provides a powerful tool for breaking down cognitive processes and revealing subtle differences between clinical groups.
Further research examining multiple disorders simultaneously may help clarify the shared and distinct mechanisms underlying neurodevelopmental conditions.

While more research is needed, this study provides evidence that seemingly distinct neurodevelopmental disorders may share some common underlying brain differences. This perspective could potentially lead to new approaches for understanding and treating these conditions in the future.