Ruhr-University, Bochum

Asymmetries in visuospatial processing in birds

by

Patrick Vollmar

Contents

Abstract 3

Introduction 4

Methods 9

Results 14

Discussion 19

References 24

Abstract

Cerebral asymmetries are a fundamental principle of vertebrate brain architecture. These asymmetrical structures are most likely beneficial for various kinds of information processings. Research has shown that the avian brain is highly visually-lateralized. Results display a left hemisphere/right eye advantage in pigeons for object processing. Unfortunately, findings on visuospatial lateralization are ambiguous. In chicks also a left hemisphere dominance for object processing has been shown whereas the right hemisphere is more probable to elicit high performances in visuospatial tasks. Inconsistently, homing pigeons revealed a left-hemispheric superiority for visuospatial orientation. We investigated visuospatial processing in pigeons (Columba livia) with a new experimental paradigm. The subjects were confined in a box with their neck and head protruding through a central circular opening. This opening was surrounded by sixteen concentrically arranged food positions each containing one piece of grain the animals had to peck at. Pigeons were tested alternately under monocular (left/right) and binocular conditions. We measured the time the subjects needed to peck all grains and the extent of visual scanning, operationalized by crossing the circular segments with their head. Although both monocular conditions did not differ with respect to the time needed to finish the task, right-seeing animals needed fewer scans to finish the task. Remarkably, both monocular conditions did not reveal significant differences in number of divers, number of peckfailures and number of direction changes. These findings display a higher efficiency of left hemispheric visuospatial processing. Left-seeing pigeons needed more scans per time than right-seeing birds to consume the grains. In summary, the superiority of the right hemisphere in spatial tasks is not an universal phenomenon of vertebrate brain architecture.

Keywords: Lateralization, spatial represenation, visuospatial processing

Introduction

The present study investigates the effects of cerebral asymmetries on visuospatial processing in the avian brain. The avian brain seems to be highly suitable for research on lateralization patterns in vertebrates. Eventually, the question might arise why the effects of asymmetry in vertebrates are focus of investigation in psychological research. Many neuronal disorders (schizophrenia, autism, etc.) are proved to result from lateralization patterns deviating from the normal structure (Highley et al. 2002). Due to the fact that nearly all cognitive functions are lateralized lateralization is one of the most fundamental principles of the brain providing optimal processing and integration of information (Rogers 2000). Unfortunately, this phenomenon has been claimed to be exclusively human for several years. Today, it is known that lateralization is widespread among vertebrates and we also know that specifcally the avian brain is predestined to research on due to particular ontogenetic factors. A lot of research has been conducted e.g. on the pigeons′ visual system and the cerebral lateralization of information processing, but investigations primarely focus on visual discrimination tasks (e.g. Skiba et al. 2001) and working-memory tasks (e.g. Prior and Güntürkün 2001). This study intends to provide more information on the spatial representation of visual stimuli in pigeons. Unfortunately, asymmetry research has neglected the question in what way the pigeon brain is lateralized with regard to visuospatial processing. Especially when investigating the effects of lateralization on spatial representation mainly experiments on homing pigeons have been conducted (Ulrich et al. 1999). In the subsequent paragraphs the characteristic features of the avian brain lateralization are revealed in detail.

The avian visual system

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