Higher order spectrum analysis of long range lateral interactions: Cat single units and human veps

A. M. Norcia, U. Polat, T. Kasamatsu, K. Mizobe, Y. Tang

Research output: Contribution to journalArticlepeer-review

Abstract

Purpose. To study spatial interactions mediated by the non-classical surrounds of single-unit receptive fields in cat striate cortex and their possible correlates in the human VEP. Methods. The display comprised a central Gabor patch modulated at frequency F1. Immediately above and below were another two Gabors that were modulated in synchrony at a different frequency, F2. In the cat, the central patch was presented within the classical receptive field (CRF) of isolated single units. The flanking patches were presented outside the CRF and when presented alone they did not elicit spikes. Similar stimuli were presented to human observers whose VEP was recorded from surface electrodes. Single unit and VEP records were analyzed with a new, high SNR non-linear spectrum analysis (time-averaged bispectrum; Tang and Norcia, 1995; IEEE EMBS Proc.). Results. When the central and flanking patches were presented together, strong non-linear interaction was observed in the power spectrum and bispectrum at frequencies related to nF1±mF2 in both the single units and human VEPs. Interactions were largest when the gratings were co-axial and col linear and were much smaller or non-existent for co-oriented but non-coaxial patterns. Conclusions. Laterally displaced stimuli interact in an orientation and configuration specific fashion, with collinearity being a particularly potent trigger feature. These interactions, recordable from the scalp in humans, may have their basis in non-linear surround mechanisms that modulate the activity of the classical receptive fields of cells in striate cortex. Bispectrum analysis, which is based on third-order statistics, provides much higher SNR than spectrum analysis procedures based on second order-statistics (FFT, adaptive filtering.).

Original languageEnglish
Pages (from-to)S483
JournalInvestigative Ophthalmology and Visual Science
Volume37
Issue number3
StatePublished - 15 Feb 1996
Externally publishedYes

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