On language laterality in normal dextrals and sinistrals: results from the bilateral object naming latency task

Area of Science:

• Neuroscience
• Cognitive Psychology
• Psycholinguistics

Background:

• Previous research by Rasmussen and Milner (1977) estimated left hemisphere dominance in 96% of dextrals and 70% of sinistrals based on epileptic patients with left hemisphere lesions.
• These estimates have been widely accepted for normal populations, influencing theories of brain lateralization.

Purpose of the Study:

• To investigate the prevalence of left hemisphere dominance in healthy dextral and sinistral individuals using a validated task.
• To re-evaluate the accuracy of previous estimates for left hemisphere dominance, particularly in sinistral populations.

Main Methods:

• Administered the Bilateral Object Naming Latency Task, a verbal tachistoscopic test with strong psychometric properties.
• Tested 188 healthy dextral and 72 healthy sinistral participants.

Main Results:

• Left hemisphere dominance was observed in 93.6% of dextrals and 80.3% of sinistrals.
• The findings suggest that the previously estimated 70% left-dominance for sinistrals may be an underestimation by approximately 10%.

Conclusions:

• The study validates high left hemisphere dominance in dextrals and indicates a higher prevalence in sinistrals than previously reported.
• Bilateral dominance appears to be less common in normal sinistrals compared to epileptic sinistrals studied by Rasmussen and Milner.