Several functions have been proposed for the avian GLv (color vision, pupillary reflex, optomotor mechanisms). In the present paper we have examined the role of the GLv in optomotor responses. For this purpose, horizontal and vertical optokinetic nystagmus (OKN) were quantified in response to different stimulation velocities, before and after chemical (kaïnic acid) lesions. Unilateral lesion of the GLv produced a marked increase of the horizontal OKN gain when the eye contralateral to the lesion was stimulated in the temporonasal (T-N) direction and, to a lesser extent, when the ipsilateral eye was stimulated in the naso-temporal (N-T) direction. Biocular integration was reduced after the lesion, since the biocular stimulation corresponding to these two monocular stimulations (ipsiversive to the lesion) produced only a moderate gain increase. When stimulations were delivered in the opposite direction (contraversive to the lesion), the horizontal OKN gain was slightly increased for the N-T monocular stimulation of the eye contralateral to the lesion, but was unchanged for other stimulations. A bilateral lesion of the GLv provoked only a slight increase of the horizontal OKN gain. The vertical OKN was not affected by the GLv lesions. Thus, the GLv system is probably involved in the modulation of optomotor responses and could mediate visuo-optokinetic interactions, each nucleus (and its associated system) exerting an inhibitory (or disfacilitatory) effect on the horizontal OKN in one direction.

We discuss the concept of Enaction as originally proposed by Varela. We attempt to exemplify through two specific topics, sensory ecology and behavior, as well as physiological and behavioral ecology, on which the enactive approach is based. We argue that sensory physiology allows us to explore the biological and cognitive meaning of animal ‘private’ sensory channels, beyond the scope of our own sensory capacity. Furthermore, after analyzing the interplay between factors that may impose limits upon an animal’s use of time and energy, we call for a program of research in integrative and comparative biology that simultaneously considers evolutionary ecology (including physiological and behavioral ecology) and neurobiology (including cognitive mechanisms as well structural design). We believe that this approach represents a shift in scientific attitude among biologists concerning the place of biological and ecological topics in studies of integrative and comparative biology and biological diversity and vice versa.

Pigeons were trained to discriminate between spectral lights and additive mixtures in the 350–560 nm spectral range using a successive “autoshaping” discrimination procedure [introduced in Palacios, Martinoya, Bloch & Varela, Vision Research, 30, 587–596 (1990)]. Dichromatic mixtures were found in the short and near UV region, but not in the middle-wave region. Our results suggest that color vision in the pigeon involves the active participation of five different primary mechanisms, which are differentially active in the yellowand red-sensitive retinal fields.

Key words: animal psychophysics, pigeon, color matching, uv vision, visual pigments, pentachromacy

One of the most eminent neuroscientists recently passed away in Paris. Professor Francisco Varela was a scholar that approached science with a remarkably broad and integrative perspective, deeply contributing to a diversity of fields, from mathematics to epistemology, from immunology to neuroscience. He was strongly influenced by Buddhism and actively participated in unraveling the relationship between science and spirituality. This article introduces a special edition of Biological Research dedicated to the memory of this great man. It contains a collection of valuable contributions by various authors who collaborated with Varela at different moments of his outstanding scientific career. Their articles cover most of the fields in which he made contributions.

Upshot: We argue that the notion of basic perception could help to develop a general enactivist account of perception, without compromising the compatibility between our approach to this theory and the notion of weak representation. To support this, we elaborate on the contextual and normative aspects of our enactivist proposal, on perception, and on how these aspects may be crucial for understanding misrepresentation and comparability.

Context: Part of Varela’s work focused on the study of visual perception, particularly on the grounds of an enactivist theory of vision. Problem: Varela held that the problem of misrepresentation and the comparability of visual experience were crucial. We live with other creatures in sensory worlds that are not tractable, so could we share color-similar experiences? We are still missing an integrative enactive framework to tackle the problems of misrepresentation and comparability related to animal color experience. Method: We carried out a literature survey to draw attention to the status of the enactivist theory of vision and to explore how the problems of misrepresentation and comparability may be tackled. Results: As shown, philosophy and computational science have recently incorporated concepts from neurobiology that close gaps between disciplines and support aspects of the enactivist approach of vision. Implications: Epistemological problems related to perception are here tackled, considering some controversial assumptions related to vision. We argue that an enactivist theory of visual perception may not only clarify the problematic consequences of those assumptions, but also fruitfully guide future philosophical and empirical research on this topic. Constructivist content: The presence of singular “visual channels”, as well as physical, sensorimotor and evolutionary factors, constrains our own perceptual experience as proposed by enactivism.

Key words: Enaction, perception, misrepresentation, comparability, high color space dimensionality, objectivism, subjectivism, computational science

Pigeons were trained to discriminate between spectral lights and additive mixtures in the 580–640 nm range. Two behavioral procedures were used: (I) a simultaneous instrumental discrimination and (II) successive “autoshaping” discrimination. Pigeons were able to make color mixture matches within this spectral range with satisfactory precision. Matchings determined by the animal correspond well to those predicted on the basis of the spectral sensitivities of two (or even three) pigment-droplet combinations present in the pigeon retina.

Key words: color psychophysics, pigeon, color mixture, visual pigments, oil droplets, autoshaping

The spectral sensitivities of retinal cones isolated from goldfish (Carassius auratus) retinas were measured in the range 277–737 nm by recording membrane photocurrents with suction pipette electrodes (SPE). Cones were identified with lmax (9S.D.) at 62396.9 nm, 53794.7 nm, 44797.7 nm, and about 356 nm (three cells). Two cells (lmax 572 and 576 nm) possibly represent genetic polymorphism. A single A2 template fits the a-band of P4472, P5372, and P6232. HPLC analysis showed 4% retinal:96% 3-dehydroretinal. Sensitivity at 280 nm is nearly half that at the lmax in the visible. The lmax of the b-band (in nm) is a linear function of the lmax of the a-band and follows the same relation as found for A1-based cone pigments of a cyprinid fish.

Key words: Goldfish, Carassius, Cones, Dehydroretinal, Spectral sensitivity, Visual pigment template spectra, Porphyropsin, Photocurrents