S cones expressing the short wavelength-sensitive type 1 (SWS1) class of visual pigment generally form only a minority type of cone photoreceptor within the vertebrate duplex retina. Hence, their primary role is in color vision, not in high acuity vision. In mammals, S cones may be present as a constant fraction of the cones across the retina, may be restricted to certain regions of the retina or may form a gradient across the retina, and in some species, there is coexpression of SWS1 and the long wavelength-sensitive (LWS) class of pigment in many cones. During retinal development, SWS1 opsin expression generally precedes that of LWS opsin, and evidence from genetic studies indicates that the S cone pathway may be the default pathway for cone development. With the notable exception of the cartilaginous fishes, where S cones appear to be absent, they are present in representative species from all other vertebrate classes. S cone loss is not, however, uncommon; they are absent from most aquatic mammals and from some but not all nocturnal terrestrial species. The peak spectral sensitivity of S cones depends on the spectral characteristics of the pigment present. Evidence from the study of agnathans and teleost fishes indicates that the ancestral vertebrate SWS1 pigment was ultraviolet (UV) sensitive with a peak around 360 nm, but this has shifted into the violet region of the spectrum (>380 nm) on many separate occasions during vertebrate evolution. In all cases, the shift was generated by just one or a few replacements in tuning-relevant residues. Only in the avian lineage has tuning moved in the opposite direction, with the reinvention of UV-sensitive pigments.

Almost 40 years ago, Davida Teller developed the forced-choice preferential looking method for studying infant visual capabilities and used it to study infant color vision. About 10 years ago, she used infant looking preferences to study infant color perception. Here, we examine four data sets in which the infant looking preference was measured using a wide range of saturated colors. Three of those data sets, from papers by Marc Bornstein and by Davida Teller and Anna Franklin and their respective collaborators, were fit successfully using MacLeod and Boynton's model of the equiluminant plane in color space, in spite of the varied luminances used in those studies. A fourth data set, from a paper by Zemach, Chang, and Teller, was less well fit by that model. Apparently, infants are able to ignore luminance, and pay attention just to the color of stimuli. These results are discussed in the context of Davida Teller's work on the philosophy of vision science.

Acetylcholine is present in and released from starburst amacrine cells in the inner plexiform layer (IPL), but its role in retinal function except, perhaps, in early development, is unclear. Nicotinic acetylcholine receptors are thought to be present on ganglion, amacrine, and bipolar cell processes in the IPL, and it is known that acetylcholine increases the spontaneous and light-evoked responses of retinal ganglion cells. The effects of acetylcholine on bipolar cells are not known, and here we report the effects of nicotine on the b-wave of the electroretinogram in larval zebrafish. The b-wave originates mainly from ON-bipolar cells, and the larval zebrafish retina is cone-dominated. Only small rod responses can be elicited with dim lights in wild-type larval zebrafish retinas, but rod responses can be recorded over a range of intensities in a mutant ( n o optokinetic response f ) fi sh that has no cone function. We fi nd that nicotine strongly enhances cone-driven b-wave response amplitudes but depresses rod driven b-wave response amplitudes without, however, affecting rod- or cone-driven b-wave light sensitivity.

Monocular deprivation (MD) by lid suture is one of the classic paradigms for the study of developmental plasticity in the cerebral cortex, and we have detailed knowledge of its anatomical and physiological consequences as well as underlying molecular and cellular mechanisms. However, the effects of other forms of manipulating visual input through one eye on the functional architecture of the primary visual cortex (V1) have not yet been examined directly. We compared MD by lid suture with the effects of daily monocular lens wear using either a frosted lens or a neutral density (ND) filter. We used optical imaging of intrinsic signals and visually evoked potentials (VEPs) to assess responses in V1 to monocular stimulation. We found that loss of stimulus contrast through monocular frosted lens wear resulted in marked takeover of cortical territory by the nondeprived eye (NDE) similar to that caused by classic MD, and in virtual absence of orientation-selective responses following stimulation of the deprived eye (DE). Furthermore, amplitudes of VEPs in response to gratings of a range of spatial frequencies were significantly reduced in the DE compared to the NDE. In contrast, differences in luminance between two eyes caused by an ND filter in front of one eye did not affect ocular dominance and orientation maps, and there was no significant difference in the amplitude of VEPs elicited through the two eyes. Our results are consistent with previous electrophysiological studies in demonstrating that binocular pattern information is necessary to maintain normal functional maps in both eyes, while reduced luminance in one eye has little effect on the overall functional architecture and visual responses in V1.

Retinal ganglion cells receive excitatory synapses from bipolar cells and inhibitory synapses from amacrine cells. Previous studies in primate suggest that the strength of inhibitory amacrine input is greater to cells in peripheral retina than to foveal (central) cells. A comprehensive study of a large number of ganglion cells at different eccentricities, however, is still lacking. Here, we compared the amacrine and bipolar input to midget and parasol ganglion cells in central and peripheral retina of marmosets (Callithrix jacchus). Ganglion cells were labeled by retrograde filling from the lateral geniculate nucleus or by intracellular injection. Presumed amacrine input was identified with antibodies against gephyrin; presumed bipolar input was identified with antibodies against the GluR4 subunit of the AMPA receptor. In vertical sections, about 40% of gephyrin immunoreactive (IR) puncta were colocalized with GABAA receptor subunits, whereas immunoreactivity for gephyrin and GluR4 was found at distinct sets of puncta. The density of gephyrin IR puncta associated with ganglion cell dendrites was comparable for midget and parasol cells at all eccentricities studied (up to 2 mm or about 16 degrees of visual angle for midget cells and up to 10 mm or >80 degrees of visual angle for parasol cells). In central retina, the densities of gephyrin IR and GluR4 IR puncta associated with the dendrites of midget and parasol cells are comparable, but the average density of GluR4 IR puncta decreased slightly in peripheral parasol cells. These anatomical results indicate that the ratio of amacrine to bipolar input does not account for the distinct functional properties of parasol and midget cells or for functional differences between cells of the same type in central and peripheral retina.

The validity of the Barten theoretical model for describing the vertebrate spatial contrast sensitivity function (CSF) and acuity at scotopic light levels has been examined. Although this model (which has its basis in signal modulation transfer theory) can successfully describe vertebrate CSF, and its relation to underlying visual neurophysiology at photopic light levels, significant discrepancies between theory and experimental data have been found at scotopic levels. It is shown that in order to describe scotopic CSF, the theory must be modified to account for important mechanistic changes, which occur as cone vision switches to rod vision. These changes are divided into photon management factors [changes in optical performance (for a dilated pupil), quantum efficiency, receptor sampling] and neural factors (changes in spatial integration area, neural noise, and lateral inhibition in the retina). Predictions of both scotopic CSF and acuity obtained from the modified theory were found to be in good agreement with experimental values obtained from the human, macaque, cat, and owl monkey. The last two species have rod densities particularly suited for scotopic conditions.

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Amacrine cells are a morphologically and functionally diverse group of inhibitory interneurons. Morphologically, they have been divided into approximately 30 types. Although this diversity is probably important to the fine structure and function of the retinal circuit, the amacrine cells have been more generally divided into two subclasses. Glycinergic narrow-field amacrine cells have dendrites that ramify close to their somas, cross the sublaminae of the inner plexiform layer, and create cross talk between its parallel ON and OFF pathways. GABAergic wide-field amacrine cells have dendrites that stretch long distances from their soma but ramify narrowly within an inner plexiform layer sublamina. These wide-field cells are thought to mediate inhibition within a sublamina and thus within the ON or OFF pathway. The postsynaptic targets of all amacrine cell types include bipolar, ganglion, and other amacrine cells. Almost all amacrine cells use GABA or glycine as their primary neurotransmitter, and their postsynaptic receptor targets include the most common GABA(A), GABA(C), and glycine subunit receptor configurations. This review addresses the diversity of amacrine cells, the postsynaptic receptors on their target cells in the inner plexiform layer of the retina, and some of the inhibitory mechanisms that arise as a result. When possible, the effects of GABAergic and glycinergic inputs on the visually evoked responses of their postsynaptic targets are discussed.

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In what ways is mammalian vision--and in particular, human vision--efficiently adapted to its ecology? We suggest that human visual artwork, which is made for the human eye, holds clues that could help answer this question. Paintings are readily perceived as representations of natural objects and scenes, yet statistical relationships between natural images and paintings are nontrivial. Although spatial frequency content is generally similar for art and natural images, paintings cannot reproduce the dynamic range of luminance in scenes. Through a variety of image manipulations designed to alter image intensity distributions and spatial contrast, we here investigate the notion that artists' representational strategies can efficiently capture salient features of natural images, and in particular, of faces. We report that humans perform near flawless discrimination of faces and nonfaces in both paintings and natural images, even for stimulus presentation durations of 12 ms. In addition, contrast negation and up-down inversion have minimal to no effect on performance for both image types, whereas 1/f noise addition significantly affects discrimination performance for art more than for natural images. Together, these results suggest artists create representations that are highly efficient for transmitting perceptual information to the human brain.