The optic tectum of pit vipers (Crotalinae) contains a layer of infrared-sensitive neurons subjacent to the visual layer; these indirectly receive input from the facial pit organs. They respond transiently to the appearance or motion of warm objects within their 25 degrees to 70 degrees excitatory receptive fields (some have inhibitory regions) and presumably allow the snake to orient or strike toward prey. The infrared and visual spatiotopic tectal maps have similar but not identical axes; the infrared magnification is greater than that for vision. Bimodal neurons have receptive fields for each modality that reflect the disparity of the two maps. This finding suggests that (i) during development the infrared and visual fibers spread out independently to fill available tectal sites and (ii) bimodal neurons form local connections without regard to establishing spatial correspondence between the two modalities.

SUMMARY1. The psychophysical spectral sensitivity of cats was assessed using a two-choice visual discrimination task by determining increment thresholds and critical flicker frequency on white and chromatic backgrounds.2. For large increments, on 0 0, 0 3 and 3 0 cd/M2 white backgrounds, the cats were most sensitive to 497 nm indicating that these backgrounds are scotopic. On 30 and 300 cd/M2 white backgrounds, the cats were most sensitive to about 454 and 561 nm indicating that these backgrounds are photopic. Sensitivity to intermediate wave-lengths indicated independent action of 'blue' and 'green' cones.3. For large increments, thresholds on photopic yellow and magenta backgrounds indicated the additive influence of 'blue' and 'green' cones.4. Spectral sensitivity functions obtained with a critical flicker frequency criterion of 10 Hz on a 30 cd/M2 white background reflected only the activity of the 'green' cone while at 20 Hz the function reflected an additive contribution of both 'blue' and 'green' cones.5. For small increments, on a 30 cd/M2 white or 96 cd/M2 orange background, sensitivity reflected only the activity of the 'green' cone.6. The cat's photopic spectral sensitivity is influenced by the psychophysical test upon which it is based in a manner that is similar to what has been found for other vertebrates. No evidence was found for a 500 nm mechanism active at photopic levels.

No abstract

No abstract

No abstract