Binocular interaction in normal vision studied by pattern-reversal visual evoked potentials (PR-VEPS)

  • Summa A. di 
  • Polo A. 
  • Tinazzi M. 
  • Zanette G. 
  • Bertolasi L. 
  • Bongiovanni L. G. 
  • Fiaschi A. 
Original Articles
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Accepted:

Abstract

Monocular and binocular visual evoked potentials (VEPs) in response to different check sizes (15-21-38-84 minutes of arc) were studied in 14 subjects with normal visual acuity and stereopsis.

The binocular VEP amplitude is slightly higher than the VEP amplitude on stimulation of the “better eye” and significantly higher than the VEP amplitude on stimulation of the “worse eye”; this effect is observed using small checks and almost exclusively involves N75-P100.

Both the N75 and P100 peaks occur earlier after binocular than monocular stimulation. The shortening of the N75 mean latency is significantly greater than that of the P100 mean latency when larger check sizes are used.

The mean latency of the N145 potential is not significantly different in monocular and binocular stimulus conditions. The slight summation effect and latency shortening in the binocular VEPs are not consistent with the hypothesis that it is the sum of separate monocular signals originating from the visual cortex that gives rise to the response. The early components of both monocular and binocular VEPs are thought to be of post-synaptic origin (outside layer 4c of area 17), where the imputs become mixed so that most cells receive information from both eyes.

The amplitude enhancement of binocular VEPs, which mainly occurs when using small checks, may be related to the increase in the total amount of cortical activity representing the macular region; this may account for binocular superiority in fine spatial resolution.

The latency shortening in binocular conditions can be explained by considering that the critical determinant of the latency is the fundamental spatial frequency of the pattern. When coarse patterns are used, their effectiveness in parafoveal stimulation may affect the VEPs, with a significant contribution coming from the more peripheral retina. The enlargement of the visual field when the eyes see simultaneously may therefore further reduce the latency of the response when using the larger checks suitable for eccentric stimulation.

Key Words

VEPs Binocular vision Monocular vision Visual acuity Stereopsis 

Sommario

Abbiamo studiato i PEV-pattern da stimolo monoculare e binoculare in 14 soggetti con normale acuità visiva e stereopsi, utilizzando quadrati con diverse grandezze angolari di stimolo (15, 21, 38, 84 minuti d'arco).

L'ampiezza ottenuta da stimolo binoculare à leggermente maggiore di quella ottenuta dall' “occhio migliore”; questo effetto è osservato usando quadrati piccoli e quasi esclusivamente per la N75-P100. Le latenze della N75 e della P100 sono più precoci in seguito a stimolo binoculare rispetto allo stimolo monoculare. L'anticipo della latenza media della N75 è significativamente maggiore di quello della P100 utilizzando quadrati di stimolo più grandi. La latenza media della N145 non si modifica in modo significativo da stimolo binoculare rispetto al monoculare. L'effetto di lieve sommazione e l'anticipo della latenza nel PEV binoculare non sono in accordo con l'ipotesi che segnali monoculari separati si sommino nella corteccia visiva per dare origine alla risposta. Le componenti precoci del PEV monoculare e binoculare si pensa siano di origine post-sinaptica, fuori dallo strato 4c dell'area 17, dove la maggior parte delle cellule riceve informazioni da entrambi gli occhi.

L'incremento in ampiezza del PEV binoculare, che si evidenzia soprattutto utilizzando i quadrati più piccoli, si può correlare all'area retinica selezionata, alla sua rappresentazione corticale e all'orientamento del campo elettrico di superficie. L'anticipo della latenza da stimolo binoculare, più evidente utilizzando grandezze angolari elevate, può essere spiegato considerando le correlazioni esistenti tra frequenza spaziale fondamentale del pattern ed eccentricità retinica. L'allargamento del campo visivo nella visione binoculare può inoltre ridurre la latenza della risposta quando si usano quadrati più grandi adatti alla stimolazione periferica.

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Copyright information

© Masson S.p.A. 1997

Authors and Affiliations

  • Summa A. di 
    • 1
  • Polo A. 
    • 1
  • Tinazzi M. 
    • 1
  • Zanette G. 
    • 1
  • Bertolasi L. 
    • 1
  • Bongiovanni L. G. 
    • 1
  • Fiaschi A. 
    • 1
  1. 1.Dipartimento di Scienze Neurologiche e della Visione, Sezione di NeurologiaUniversità di Verona, Policlinico Borgo RomaVeronaItaly

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