Localization of Free-Field Sound Sources in the Chronic Phase of Mild Ischemic Stroke.
Mathias Dietz, Anna Dietze, Peter Sörös and 2 others
Most mild stroke survivors localized free-field sounds as accurately as controls.
Four of fourteen gave responses clustered at only a few fixed positions rather than tracking the actual source direction, mostly for low-frequency sounds. Three of those four had right-hemispheric lesions.
Key findings
1The stroke group as a whole did not differ significantly from the control groups in localization accuracy across any of the three noise conditions.
2Four of the 14 stroke patients and one age-matched control showed a qualitatively different pattern, responding at only two or three fixed positions rather than the actual source direction, predominantly for low-frequency and broadband sounds. Three of the four stroke patients had right-hemispheric lesions in the cerebellum, thalamus, or basal ganglia.
3In three patients the localization pattern did not match the lateralization pattern recorded in the same session: two had a lateralization bias but normal localization, and one had normal lateralization but a strongly bimodal localization response.
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How it was doneWhat they found
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What it does not show
Fourteen stroke patients and five age-matched controls is a very small group. The study cannot tell whether the four atypical localizers were affected by their stroke or by something else, because one control showed the same pattern without a confirmed stroke and had no brain scan. Only the chronic phase was tested. There is no localization data from the acute or subacute phase, so it is unknown whether these deficits were present earlier and recovered, or appeared later. The control group had no MRI, cognitive testing, or depression screening, so their brain and hearing status is less well characterized than the patients'. With 14 patients, statistical power is very low. The paper notes that significance at the 0.05 level requires a correlation coefficient above 0.4, which is a high bar for a sample this size.
Declared interests
Funded by the European Research Council (Horizon 2020) and the German Research Foundation. The authors declare no commercial or financial conflicts of interest.
The easy way to misread this
Do not read the four atypical localizers as proof that mild stroke impairs sound localization. The group-level comparison showed no significant difference from controls, and one of the five atypical listeners was a control subject with no confirmed stroke. With 14 patients and no brain scans for the controls, the study cannot separate a stroke effect from other age-related or undiagnosed causes.
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