All right reserved: Daniele Marzoli1 and Luca Tommasi1 Contact Information (1) Department of Biomedical Sciences, University “G. d’Annunzio”, Blocco A, Via dei Vestini 29, 66013 Chieti, Italy Published on http://blogsetie.blogspot.com

1. Naturwissenschaften (2009) 96:1099–1106
DOI 10.1007/s00114-009-0571-4
ORIGINAL PAPER
Side biases in humans (Homo sapiens): three ecological
studies on hemispheric asymmetries
Daniele Marzoli & Luca Tommasi
Received: 16 January 2009 / Revised: 20 May 2009 / Accepted: 26 May 2009 / Published online: 20 June 2009
# Springer-Verlag 2009
Abstract Hemispheric asymmetries and side biases have Mandal et al. 2000; Brancucci et al. 2009) but also in many
been studied in humans mostly in laboratory settings, and other vertebrate species (Rogers 1999; Rogers and Andrew
evidence obtained in naturalistic settings is scarce. We here 2002; Tommasi 2009). Among the many classes of
report the results of three studies on human ear preference lateralized behaviors discovered thus far, side biases during
observed during social interactions in noisy environments, interactions between conspecifics have been observed both
i.e., discotheques. In the first study, a spontaneous right-ear in lower and in higher vertebrates (Bisazza et al. 1998;
preference was observed during linguistic exchange be- McKenzie et al. 1998; Sovrano et al. 2001; Zucca and
tween interacting individuals. This lateral bias was con- Sovrano 2008), as well as in humans (Turnbull and Lucas
firmed in a quasi-experimental study in which a confederate 2000; Güntürkün 2003) and in other primates (for a review,
experimenter evoked an ear-orienting response in bystand- see Damerose and Vauclair 2002).
ers, under the pretext of approaching them with a whispered One of the best-known asymmetries in humans is the
request. In the last study, subjects showed a greater right-ear dominance for listening to verbal stimuli (e.g.,
proneness to meet an experimenter’s request when it was Bryden 1988; Kimura 1961), which is associated with a
directly addressed to the right rather than the left ear. Our general right-ear preference in tasks requiring the use of a
findings are in agreement both with laboratory studies on single ear (e.g., Ida and Mandal 2003; Porac and Coren
hemispheric lateralization for language and approach/ 1981). Many laboratory studies and particularly those
avoidance behavior in humans and with animal research. employing the dichotic listening method (the simultaneous
The present work is one of the few studies demonstrating presentation of two different stimuli to the ears) have
the natural expression of hemispheric asymmetries, show- evidenced a right-ear advantage in several linguistic tasks.
ing their effect in everyday human behavior. Since the early reports of Kimura (1961), this advantage
has been documented in right and left handers, in adults and
Keywords Side bias . Ear preference . Behavioral children and in both sexes (Bryden 1988; Hiscock 1988;
lateralization . Communication . Hemispheric asymmetries . Hugdahl et al. 1990). Furthermore, a small but significant
Approach/avoidance behavior . Homo sapiens right-ear advantage was reported for recognition of words
presented to the left or right ear in the presence of
continuous binaural white noise (Young and Ellis 1980).
Introduction According to Kimura (1967), the right-ear advantage in
dichotic listening tasks with verbal stimuli reflects the left
It is now well-established that perceptual and motor hemisphere superiority for processing verbal information.
asymmetries exist not only in humans (for reviews, see This depends on the fact that the contralateral auditory
pathway suppresses the ipsilateral pathway, so that the
D. Marzoli : L. Tommasi (*) right-ear input to the left hemisphere would be advantaged
Department of Biomedical Sciences, University “G. d’Annunzio”, with respect to the left ear input to the same hemisphere
Blocco A, Via dei Vestini 29,
66013 Chieti, Italy (Kimura 1967). Moreover, the transfer of the input from the
e-mail: luca.tommasi@unich.it left ear to the left hemisphere across the corpus callosum