ORIGINAL PAPER

Side biases in humans (Homo sapiens): three ecologicalstudies 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 havebeen studied in humans mostly in laboratory settings, andevidence obtained in naturalistic settings is scarce. We herereport the results of three studies on human ear preferenceobserved during social interactions in noisy environments,i.e., discotheques. In the first study, a spontaneous right-earpreference was observed during linguistic exchange be-tween interacting individuals. This lateral bias was con-firmed in a quasi-experimental study in which a confederateexperimenter evoked an ear-orienting response in bystand-ers, under the pretext of approaching them with a whisperedrequest. In the last study, subjects showed a greaterproneness to meet an experimenter’s request when it wasdirectly addressed to the right rather than the left ear. Ourfindings are in agreement both with laboratory studies onhemispheric lateralization for language and approach/avoidance behavior in humans and with animal research.The present work is one of the few studies demonstratingthe natural expression of hemispheric asymmetries, show-ing their effect in everyday human behavior.

Keywords Side bias . Ear preference . Behaviorallateralization . Communication . Hemispheric asymmetries .

Approach/avoidance behavior . Homo sapiens

Introduction

It is now well-established that perceptual and motorasymmetries exist not only in humans (for reviews, see

Mandal et al. 2000; Brancucci et al. 2009) but also in manyother vertebrate species (Rogers 1999; Rogers and Andrew2002; Tommasi 2009). Among the many classes oflateralized behaviors discovered thus far, side biases duringinteractions between conspecifics have been observed bothin lower and in higher vertebrates (Bisazza et al. 1998;McKenzie et al. 1998; Sovrano et al. 2001; Zucca andSovrano 2008), as well as in humans (Turnbull and Lucas2000; Güntürkün 2003) and in other primates (for a review,see Damerose and Vauclair 2002).

One of the best-known asymmetries in humans is theright-ear dominance for listening to verbal stimuli (e.g.,Bryden 1988; Kimura 1961), which is associated with ageneral right-ear preference in tasks requiring the use of asingle ear (e.g., Ida and Mandal 2003; Porac and Coren1981). Many laboratory studies and particularly thoseemploying the dichotic listening method (the simultaneouspresentation of two different stimuli to the ears) haveevidenced a right-ear advantage in several linguistic tasks.Since the early reports of Kimura (1961), this advantagehas been documented in right and left handers, in adults andchildren and in both sexes (Bryden 1988; Hiscock 1988;Hugdahl et al. 1990). Furthermore, a small but significantright-ear advantage was reported for recognition of wordspresented to the left or right ear in the presence ofcontinuous binaural white noise (Young and Ellis 1980).

According to Kimura (1967), the right-ear advantage indichotic listening tasks with verbal stimuli reflects the lefthemisphere superiority for processing verbal information.This depends on the fact that the contralateral auditorypathway suppresses the ipsilateral pathway, so that theright-ear input to the left hemisphere would be advantagedwith respect to the left ear input to the same hemisphere(Kimura 1967). Moreover, the transfer of the input from theleft ear to the left hemisphere across the corpus callosum

Naturwissenschaften (2009) 96:1099–1106DOI 10.1007/s00114-009-0571-4

D. Marzoli : L. Tommasi (*)Department of Biomedical Sciences, University “G. d’Annunzio”,Blocco A, Via dei Vestini 29,66013 Chieti, Italye-mail: luca.tommasi@unich.it