Effects of Domain-Specific Noise on Visual Motion Processing in Schizophrenia

Abstract

BackgroundVisual perception impairments in schizophrenia stem from abnormal information processing. Information processing requires neural response to a stimulus (signal) against a backdrop of 1) random variation in baseline neural activity (internal noise) and sometimes irrelevant environmental stimulation (external noise). Filtering out noise is a critical aspect of information processing, and needs to be critically examined in schizophrenia.MethodsTo understand how noise in the visual system constrains perceptual processing, we devised a novel paradigm to build in both signal and external noise on same visual stimulus. Here, instead of uniformed noise, domain-specific noise—variations in stimulus speed—was introduced to evaluate the performance of schizophrenia patients in speed discrimination. Each motion stimulus—a random dot pattern (RDP) comprising 200 moving dots—included a range of speeds, drawn individually from a Gaussian distribution for each dot. The task for patients (n = 26) and controls (n = 28) was to identify which of two stimuli moved faster based on their mean speeds.FindingsPatients exhibited deficient speed discrimination at baseline, in the absence of speed noise. Their speed discrimination was further degraded in the presence of low and medium levels of external noise. In the presence of a high levels of noise, degradation of patients' speed discrimination leveled-off, resulting in similar performance to controls.ConclusionThese domain-specific noise effects on speed discrimination provide direct evidence for the existence of heightened internal noise within a specific visual motion processing domain in schizophrenia.

Intact perception of coherent motion, dynamic rigid form, and biological motion in chronic schizophrenia

“…Slaghuis et al (2007) found coherent motion deficits in schizophrenia patients for lower but not higher velocities. Chen et al (2014) found speed discrimination deficits when the target had only low or moderate amounts of speed noise. Kim, Park and Lee (2005) suggest that patients may primarily be more prone to falsely recognizing biological motion when discriminating intact and phase-scrambled point-like walkers (see also Task 3 of Kim et al, 2013).…”

Specific vulnerability of face perception to noise: A similar effect in schizophrenia patients and healthy individuals

“…The presence of external noise did interfere with non-face visual processing in schizophrenia patients (Chen et al, 2014; Kim et al, 2013; Chen et al, 2008; Chen et al, 2003; Stuve et al, 1997). While this study showed quantitative differences between the noise effects in face processing and in non-face visual processing, whether qualitative differences exist in schizophrenia remains unclear.…”

“…Previous studies have been focused on how different functional domains such as affective and non-affective processing of facial images are altered in schizophrenia patients (Heimberg et al, 1992; Gur et al, 2002; Butler et al, 2008; Chen et al, 2009; Chen et al, 2008; Silverstein et al, 2009; McBain et al, 2010; Lee et al, 2011; Yoon et al, 2006; Lee et al, 2007). Noise-filtering is essential for the processing of perceptual information including faces, and appears to be implicated in various aspects of deficient perceptual processing in schizophrenia (Chen et al, 2014; Kim et al, 2013; Chen et al, 2008). A recent study proposed heightened noise levels as a mechanism underlying abnormal facial processing in schizophrenia (Spencer et al, 2013).…”

Selectively reduced contrast sensitivity in high schizotypy

“…Our findings at high temporal frequencies might also reflect increased internal noise (decreased signal-noise ratios) in those who exhibited high schizotypy scores. In the context of schizophrenia, a recent study (Chen et al 2014) using random dot kinematograms has shown that schizophrenics exhibited significantly poorer speed discrimination across a range of speeds (5.25-13.0 deg/s) and their performance was more susceptible to the addition of noise compared to controls.…”