Binocularity in the little owl, athene noctua: II. properties of visually evoked potentials from the wulst in response to monocular and binocular stimulation with sine wave gratings

Vittorio Porciatti, Gigliola Fontanesi, Agnese Raffaelli, Paola Bagnoli

Research output: Contribution to journalArticle

16 Scopus citations

Abstract

Visually evoked potentials (VEPs) have been recorded from the Wulst surface of the little owl, Athene noctua, in response to counterphase-reversal of sinusoidal gratings with different contrast, spatial frequency and mean luminance, presented either monocularly or binocularly. Monocular full-field stimuli presented to either eye evoked VEPs of similar amplitude, waveform and latency. Under binocular viewing, VEPs approximately doubled in amplitude without waveform changes. VEPs with similar characteristics could be obtained in response to stimulation of the contralateral, but not ipsilateral, hemifield. These results suggest that a 50% recrossing occurs in thalamic efferents and that different ipsilateral and contralateral regions converge onto the same Wulst sites. The VEP amplitude progressively decreased with increase of the spatial frequency beyond 2 cycles/degree, and the high spatial frequency cut-off (VEP acuity) was under binocular viewing (8 cycles/degree) higher than under monocular (5 cycles/degree) viewing (200 cd/m2, 45% contrast). The VEP acuity increased with increase in the contrast and decreased with reduction of the mean luminance. The binocular gain in both VEP amplitude and VEP acuity was largest at the lowest luminance levels. Binocular VEP summation occurred in the medium-high contrast range. With decreased contrast, both monocular and binocular VEPs progressively decreased in amplitude and tended to the same contrast threshold. The VEP contrast threshold depended on the spatial frequency (0.6-1.8% in the range 0.12-2 cycles/degree). Binocular VEPs often showed facilitatory interaction (binocular/monocular amplitude ratio >2), but the binocular VEP amplitude did not change either by changing the stimulus orientation (horizontal vs. vertical gratings) or by inducing different retinal disparities. These results indicate that VEPs can serve as a useful tool to measure visual performance in owls under different stimulus conditions in their operative range. Under low-luminance, high-contrast conditions, binocular visual performance, compared to monocular performance appears to improve by a factor of more than √2 (probability summation). This binocular advantage occurs independent of stereopsis.

Original languageEnglish (US)
Pages (from-to)40-48
Number of pages9
JournalBrain, Behavior and Evolution
Volume35
Issue number1
DOIs
StatePublished - Jan 1 1990
Externally publishedYes

Keywords

  • Binocular interaction
  • Birds
  • Pattern visually evoked potentials
  • Visual pathways

ASJC Scopus subject areas

  • Developmental Neuroscience
  • Behavioral Neuroscience

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