Embryonic light stimulation induces different asymmetries in visuoperceptual and visuomotor pathways of pigeons

Abstract

In birds, visual object discrimination performance is lateralized with a dominance of the right eye/left hemisphere. This asymmetry is induced by embryonic light stimulation. However, visually guided behavior, even during simple object distinction tasks, is composed of different behavioral and neural modules. Therefore, the aim of the present study was to test whether all neural subsystems involved in visual discriminations are lateralized in a similar way after prehatch visual stimulation. To examine this question, two behavioral paradigms were used which reveal complementary aspects of visually guided behavior. The first was the grain Á/grit discrimination task in which no left Á/right differences in the number of pecks, but significant differences in the number of grains can be found. Therefore, grain Á/grit discrimination reveals visuoperceptual performance but not visuomotor speed. The contrary seems to be the case for a successive pattern discrimination with a VR32 schedule. Here, the hemispheres do not differ with respect to discrimination accuracy but with regard to the number of pecks emitted. Thus, successive pattern discrimination with lean VR schedules reveals hemispheric differences in visuomotor speed without testing visuoperceptual performance. Using these two paradigms a group of light and a group of dark incubated pigeons were tested. The results show that dark incubated birds evinced no asymmetry in any measure while light incubated ones were right-eye dominant in both variables. However, light incubation induced a visual left hemispheric dominance by modulating two different processes, a left-hemispheric increase of visuoperceptual processes; and a right-hemispheric decrease for visuomotor speed. Taken together these data show that embryonic light stimulation elicits visual lateralization by differently modulating visuoperceptual and visuomotor systems in both hemispheres. #

The impact of asymmetrical light input on cerebral hemispheric specialization and interhemispheric cooperation

“…Fourteen normal adult domestic pigeons (Columba livia) from local breeders as well as eight adult dark-incubated animals from lab-own breeding pairs 23 served as subjects for an operant transitive inference experiment. The animals were housed in individual cages and were kept food-deprived to ~80% of their free-feeding weight throughout the experiment.…”

“…Binocular performance, in turn, correlates with the degree of visual lateralization 18 and strongly lateralized chicken demonstrate a better ability to carry out representational learning than less-lateralized individuals 21 . Visual asymmetries develop in response to asymmetrical light stimulation as indicated by the absence of asymmetrical differentiation processes in darkincubated birds 16,22,23 . This allows us to compare the capacity of hemispheric cooperation in lateralized and non-lateralized birds, in order to investigate the impact of ontogenetic experience on the interrelations between hemispheric specialization and integration.…”

“Let There be Light!” pigeon eggs are regularly exposed to light during breeding

“…Light exposure of pigeon eggs induce the establishment of visual lateralisation with a superiority of the right eye in object discriminations, while dark incubation prevents the emergence of this asymmetry (Rogers, 1982;Skiba et al, 2002). The same result is achieved by right-sided monocular deprivation after hatching (Manns and Güntürkün, 1999b).…”

“…A detailed analysis showed that indeed, dark incubation produces the second alternative, i.e. these pigeons show no individual bias to the right or the left eye in object discriminations (Skiba et al, 2002).…”

Visual experience affects handedness

“…This asymmetrical visual stimulation importantly affects the just developing visual pathways and modulates the emergence and organisation of visuocognitive asymmetries [33]. Incubation of eggs in total darkness prevents the development of anatomical asymmetries within ascending visual pathways, while abolishing or modulating behavioural left-right differences in object discrimination [6,48,51]. Occlusion of the right eye and exposition of the left eye to light leads to a reversed visual lateralisation pattern [33].…”