Circadian Differences in the Dichotic Processing of Voicing

Male and female adult subjects (N = 112) were tested at two times (morning and afternoon) for time-of-day related shifts in linguistic processing on dichotic listening tasks using (1) a divided-attention paradigm for processing digits (0-9) and (2) a focused-attention paradigm for processing consonant-vowel (CV) combinations which were grouped according to the voiced and unvoiced stop consonants. Time-of-day effects were not evident on digits using the divided-attention paradigm. However, on CVs a predicted two-way interaction for Time-of-Day Voicing-due to superior detection of voiced stimuli in the afternoon-was evident. This effect is consistent with a circadian-linked increase in right hemisphere involvement later in the day. Implications for theory, research and educational applications are discussed.