Diurnal type and hemispheric asymmetry.

Monk and Leng (1986) postulated that Morning-types (M-types) rely more than Evening-types (E-types) on subvocalization strategies, indirectly suggesting a difference in their habitual mode of hemispheric engagement. To evaluate this hypothesis, 48 right-handed women, 24 M-types and 24 age-matched E-types, performed verbal and spatial hemifield tachistoscopic tasks and recorded oral temperature at four separate times of day. Oral temperature curves were larger in amplitude and phase delayed for E-types. Reaction time curves were slower for E-types, without M-E phase differences. Error rate curves showed significant time-of-day effects at left-visual-field verbal tasks for M-types and at right-visual-field spatial tasks for E-types, indicating a selective trend in relying on left hemispheric mode for M-types and on right hemispheric mode for E-types. Implications for circadian oscillatory control are discussed.