Lateralisation of language and spatial skills is not affected by task difficulty: a functional transcranial doppler ultrasonography investigation

We used functional transcranial Doppler ultrasonography (fTCD) to assess the effect of task difficulty on cerebral lateralisation during language and spatial tasks in typical adults. Auditory naming was used to examine language lateralisation: participants were presented with short auditory definition and asked to provide a speeded, verbal, single-word response of the defined word. Difficulty was manipulated by varying word frequency. A modified land-mark task was used to examine spatial lateralisation: participants were presented with series of backward-masked, inverted 'T' displays and asked to make a speeded response as to the left or right position of the vertical line. Difficulty was manipulated by the presentation duration and proximity of the vertical line to the centre of the display. Behavioural responses were consistent with the difficulty manipulations; for auditory naming, accuracy was higher and response times were faster for high frequency words; for the land-mark task, accuracy was higher and response times were faster for long presentation durations and wider spatial proximities. Despite the expected behavioural differentiation, fTCD lateralisation was not influenced by task difficulty for either ability.