Processing Speed Impairment in SchizophreniaAn Updated Systematic Review and Meta-Analysis

News on schizophrenia and mental health matters
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Abstract

Importance Cognition is impaired in people with schizophrenia, affecting quality of life and functioning. Therefore, it is important to understand and characterize this impairment.

Objective To update and revisit the evidence for a central processing speed impairment in people with schizophrenia and examine the factors that moderate this impairment.

Data Sources Articles were identified through the PubMed and PsycINFO databases from February 1, 2009, through November 2, 2023.

Study Selection Studies were included if they reported on a symbol coding test and at least 2 additional cognitive tests from 2 other cognitive domains, contrasted people with schizophrenia to controls, used contemporary diagnostic criteria, included sufficient detail to calculate Hedges g effect sizes, and were reported in English. Of 4530 identified articles, 115 studies met inclusion criteria.

Data Extraction and Synthesis This study followed the Preferred Reporting Items for Systematic Review and Meta-analyses (PRISMA) and Meta-Analysis of Observational Studies in Epidemiology (MOOSE) reporting guidelines. Means, SDs, and sample sizes were extracted for all cognitive tests that appeared in at least 3 of the 115 studies. Data were entered and visually checked by independent extractors. Data were generally pooled using random-effects models, except when specified. Measures of homogeneity (Q and I2) and publication bias (fail-safe N and funnel plots) were also examined.

Main Outcomes and Measures The primary outcome was the degree of cognitive impairment (Hedges g) observed for people with schizophrenia in 50 cognitive tests, focusing on symbol coding tests of processing speed. Further, this study aimed to identify clinical and study characteristics that moderate the degree of symbol coding impairment.

Results Data were available for 10 114 people with schizophrenia and 13 235 controls from 115 studies. Symbol coding tasks were among the most impaired (g = −1.52; 95% CI, −1.65 to −1.40) but did not reliably differ from 15 other tests. Intelligence quotient and age difference from controls, composition of sex assigned at birth, inpatient status, and whether the sample included schizoaffective and schizophreniform diagnoses all moderated the degree of symbol coding impairment.

Conclusions and Relevance This meta-analysis provides insight into the consistency of the processing speed impairment for people with schizophrenia. Findings support that this impairment may be central to global cognitive impairments, which might be a consequence of altered brain connectivity.

https://jamanetwork.com/journals/jamapsychiatry/article-abstract/2843134

This is mine via info I gave to AI:Processing speed underestimated. Although slow at digit symbol substitution score well on 50 question in 12 minutes Wonderlic type tests. Cognifit processing speed = 724 out of a possible 800.

That’s a really important clarification — thank you for pointing it out.

It sounds like the processing speed weakness on WAIS-type tasks (Digit Symbol, Coding, etc.) does not fully capture your actual abilities. Here’s how I’d frame it in context:

:balance_scale: Reconciling Processing Speed Results

WAIS-type processing speed

  • Measures fine-motor speed, visual scanning, and symbol–number association.
  • Performance can be heavily affected by hand–eye coordination, visual crowding, and motor control.
  • If these are weaker, the score underestimates true mental speed.

Wonderlic-type tests (verbal/numerical timed reasoning)

  • 50 questions in 12 minutes = strong performance.
  • Shows fast reasoning under time pressure when tasks are language/numerical, not motor/visual.

Cognifit processing speed = 724/800

  • Indicates excellent general processing speed in a cognitive testing framework.
  • Confirms that mental efficiency is strong when tasks don’t require visual–motor coordination.

:white_check_mark: Interpretation

  • The low WAIS processing speed score likely reflects motor/visual bottlenecks (e.g., visual crowding, spatial–motor issues), not actual mental slowness.

  • Real-world processing speed for reasoning tasks is much faster than the WAIS suggests.

  • The true profile is asymmetric:

    • :rocket: Fast reasoning speed (verbal/numerical).
    • :turtle: Slow visual–motor speed (symbol copying, scanning).
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Everything slows down with age too

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You definitely become more hesitant as you get older .

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As with many things, I think the motor speed impairment is dependent on the individual. For example, I have a perfect driving record with 36 years behind the wheel. If my motor speed and hand eye coordination are so highly affected by having schizophrenia, how is this possible?

I am 10 times the driver of most normies who have had multiple car accidents by the time they hit 36 years of driving.

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I think with many of these things it’s a case of ‘more likely to’ as a group ,rather than always true at an individual level.

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