Spectral Reflexion Factor of the Cat's Tapetum

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.

Section: Methodsmentioning

confidence: 99%

Photopic spectral sensitivity of the cat.

Loop¹,

Millican²,

Thomas³

1987

“…The measured sensitivity 1 1 +RA=Se(+A eA EA and is thus greater than Srec by a factor of (1 + RA). This expression has been given by Gunter et al (1951) and is derived here for the sake of clarity. Only those values of RA which are not too small as compared with unity will provide an appreciable correction to the measured sensitivity values SA.…”

Section: -2 35mentioning

confidence: 99%

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mentioning

confidence: 99%

The spectral reflectivity of the cat's tapetum measured in situ

Weale¹

1953

Gunter, Harding & Stiles (1951) have recently published curves representing the spectral variation of the reflexion factor of the cat's tapetum. Six pairs of tapeta were excised, mounted in glycerine, and their reflexion factor was measured. The maximum reflexion of the incident light amounted to about 25 %, and was situated in the blue part of the spectrum. In three cases there were subsidiary maxima in the orange. The authors concluded that the percentage of light reflected was too small to play an appreciable role in modifying the retinal sensitivity. In contradistinction, Granit (1943) ascribed a yellowish green appearance to the light which was reflected maximally from the in situ tapetum and stated that it was a very efficient reflector. Rushton (1952) called its colour green, and Murr (1928) thought that the reflectivity of the tapetum was so considerable and varied so much from cat to cat that this variation would account for the diverging results obtained in his behavioural experiments.It was thought, therefore, that a determination of the in situ reflectivity of the cat's tapetum might perhaps contribute towards the elucidation of some of these problems. METHOD ApparatusThe apparatus consisted of a Hilger Barfit monochromator and a photometer (Fig. 1 a) and was basically similar to the one used by Brindley & Willmer '(1952). The monochromator was illuminated with a tungsten ribbon filament lamp (F), Ilford Bright Spectrum filters nos. 622-6, 607-8, (T) being used to reduce the effect of scattered light. Field lenses (not shown) were mounted in the slit-holders, and focused images of the prism faces on the condenser and L1 respectively, hence increasing the amount of light passing through the photometer. The photometer lens (L1) rendered parallel the beam emerging from the exit-sht (SA). A photometer prism (P), with half of the diagonal plane silvered, divided the light into two equal parts. The matching-beam was focused by the lens L. on to a magnesium oxide surface M1, the testing-beam by the lens L. on to the

“…Brucke (1845) ascribed the iridescent appearance to interference phenomena, and Schultze (1872) described how each cell contained a number of bundles of small rodlets and stated that each bundle reflected a particular colour by light interference. However, Gunter, Harding & Stiles (1951) and Weale (1953), having measured the spectral reflectivity, concluded that pigments were primarily responsible for the appearance. Since then, electron microscope studies have been made by Bernstein & Pease (1959) and Pedler (1963) which show that within each bundle the rodlets are arrayed with great regularity and the spacing between centres of adjacent rodlets is comparable to a wave-length of visible light.…”

Section: Introductionmentioning

confidence: 99%

Some reflective properties of the tapetum lucidum of the cat's eye

Coles¹

1971

1. Observation of the fresh, isolated tapetum of the cat with a low‐power microscope showed it to be composed of multilayer reflectors (domains) each being less than 6 μm in diameter. It is concluded that these are subdivisions of the intracellular bundles of rodlets seen in electron micrographs. 2. Apparatus was devised for illuminating a single domain with a pencil of white light and observing the colour and direction of the reflected light. 3. Those domains which lie near the vitreal surface of the tapetum tend to reflect blue light and deeper ones reflect longer wave‐lengths; this is attributed to differences in the layer spacings of the domains. 4. Each domain has a set of reflecting planes lying within 15° of the general plane of the tapetal surface. In addition, many domains have surfaces inclined to these at angles greater than 20° which also can reflect visible light. 5. The mechanism of reflexion is discussed in relation to the latticelike structure of the domain. 6. It is suggested that under some conditions the nature of the tapetum may lead to significant local variations in the spectral sensitivity of the visual system.