Physiology & Behavior, Vol. 34, pp. 575-577. Copyright ©Pergamon Press Ltd., 1985. Printed in the U.S.A. 0031-9384/85 $3.00 + .00 Lateralization of Visually Controlled Behavior in Pigeons ONUR GUNTORKON Experimentelle Tier.psychologie, Psychologisches lnstitut, Ruhr-Universitiit Bochum, D 4630 Bochum I, FRG Received 16 August 1983 GONTORKON, O. Lateralization of visually controlled behavior in pigeons. PHYSIOL BEHAV 34(4) 575-577, 1985.- Pigeons were trained binocularly on two different successive pattern discrimination tasks. After reaching criterion they performed the tasks with either the left or the right eye occluded or with both eyes unobstructed. The number of responses emitted was greater when the fight rather than the left eye was uncovered. Also the percent correct discrimination scores were better when seeing with the right eye than with the left one. Some pigeons originally acquired the discrimination monocularly, generally using the right eye, although both eyes were uncovered. The results are discussed in relation to brain structures that may mediate this performance. Lateralization Visual system Visual discrimination learning Pigeon DESPITE an early report of left-handedness in parrots [4], lateraiization has been thought to be an exclusive attribute of higher primates. Nottebohm [15] however, showed that le- sions of a part of the left hypoglossal nerve reduced the song repertoire of male canaries by a greater amount than did lesions of the right nerve. Later studies also demonstrated that the left telencephalic vocalizational areas have a greater influence on the song production in this bird than the right ones [16]. Howard et al. [10] showed that injection of gluta- mate, a putative amino acid transmitter, into the left fore- brain hemisphere of chicks enhanced the amount of sexual and aggressive behavior and impeded auditory habituation and the visual discrimination of grain from pebbles. Similar results were also obtained with cycloheximide, an inhibitor of ribosomal protein synthesis [19]. Andrew et aL [1] found marked differences in the visual habituation of chicks de- pending on whether the stimuli were seen with the right or the left eye. In an elegant study by Rogers [19], the laterali- zation of visually guided behavior in chicks was shown to be due to the differential exposure to light of the two eyes dur- ing a critical embryonic period. The visual system of birds is particularly appropriate for studying information processing in the separate brain hemispheres. The axons of the optic nerves decussate completely at the chiasma and project to the contralateral tectum and thalamus. A tecto-thalamo-telencephalic and a thalamo-telencephalic pathway ascend mainly to the ipsilat- eral forebrain [2]. Birds do not have a corpus callosum but have instead a number of smaller commissures in which the two visual pathways recross only to a small extent to the contralateral brain hemisphere. The degree of transfer of monocularly learned information to the contralateral brain depends on the specific experimental conditions [7,20]. The aim of this study was to investigate whether laterali- zation occurs in the context of complex visual discrimination tasks. METHOD Eight experimentally naive adult homing pigeons (Col- umba livia) of local stock were used. They were maintained at 80% of their normal body weight throughout the experi- ments. A conventional Skinner-box with a single response key on which the visual stimuli were back-projected with a multi- channel microprojector was used. Rewards were delivered with a solenoid activated food-hopper, situated below the response key. A reinforcement light accompanied food re- ward. The box, which was located in a sound-attenuated chamber, was illuminated by a houselight. All relevant events were programmed with digital modular equipment, which also counted the key-pecking responses. The pecking of the white-light illuminated key was shaped using an au- toshaping procedure. When the animals had learned to associate key pecking with food reward discrimination train- ing began. Two stimuli, shown in Fig. 1, were successively projected onto the response key in a quasi-random sequence [3]. For half of the pigeons the first of the two stimuli was deemed to be correct and for the other half the second. Pecks to the correct stimulus yielded 4 sec food access. Each peck on the incorrect stimulus extended the projection time for 2 sec thus ensuring extinction of pecking to the incorrect pat- tern. Without such extension each trial lasted 20 sec. To assess the frequency of pecking to the correct and the incor- rect stimuli only the responses during the standard first 20 sec were considered. Each session consisted of 40 trials. At the beginning of the discrimination the pigeons were reinforced on a VR 4 schedule. After reaching 85% of correct responses in one session the ratio was increased to VR 8, then to VR 16 finally to VR 32. After reaching 85% of correct responses in three consecutive sessions with a VR 32 schedule the acquisition phase was completed and the pi- geons underwent surgery. While the animals were anaesthe- tized (Equithesin, 0.5 ml per 100 g bodyweight) the scalp was 575