Face processing
Why do people with schizophrenia struggle to tell faces apart?
Open access · cc by · source: Europe PMC
People with schizophrenia needed more contrast to identify faces because their visual processing was noisier, not because they used facial information less efficiently.
Study at a glance
- Design
- Case-control — Patients vs healthy controls on a two-alternative face match-to-sample task; contrast thresholds measured by staircase for upright and inverted faces at low and high external noise, fitted with a linear amplifier model
- N
- N=47 · 23 people with schizophrenia-spectrum diagnoses and 24 controls; internal-noise analyses used subsets of 20 per group (upright) and 36 participants in total (inverted)
- Population
- Medicated adults with schizophrenia, schizoaffective or schizophreniform disorder and healthy controls matched on age, education and estimated IQ, in Hamilton, Canada
- Outcome
- Face identification contrast threshold; estimated equivalent internal noise and calculation efficiency
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Key findings
People with schizophrenia had higher thresholds overall, and everyone did worse with inverted faces and with added noise; the patient deficit was similar across these conditions. Estimated internal noise was significantly higher in patients for upright faces and showed a trend in the same direction for inverted faces. Calculation efficiency did not differ between groups for either orientation, although it was lower for inverted faces in both groups.
Methodology
Twenty-three people with schizophrenia and 24 healthy controls saw a face briefly, then had to pick it out from two faces shown side by side. The contrast of the test faces was adjusted trial by trial to find the level needed for 79% correct, both for upright and upside-down faces and with or without visual noise added to the faces. Comparing thresholds with and without external noise let the researchers separate two possible causes of poor performance: more random noise inside the observer's visual system, or less efficient use of the useful information in the face.
Limitations
Internal noise could only be estimated for participants whose threshold rose with added noise, so several people per group were dropped, leaving 20 per group for upright faces and fewer for inverted faces. Only two noise levels were used, which gives rough estimates of the masking function. All patients were medicated and relatively high-functioning (matched to controls on IQ and education), so medication effects cannot be ruled out and results may not generalise; nor does the study show whether higher internal noise is specific to schizophrenia or to faces. The source of the extra noise (for example, eye jitter or neural instability) was not measured.
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