No evidence for polarization sensitivity in the pigeon electroretinogram

The electroretinographical response to flashes of linearly polarized light directed at the pigeon's yellow field was compared with that to flashes of unpolarized light. This was carried out for white light and for monochromatic light of various wavelengths, including ultraviolet. In addition, responses to slow rotation of the E-vector of polarized light were measured. Neither the presence or absence of polarization, nor the orientation of the E-vector, influenced any of the electrophysiological variables that were monitored in these experiments.

The photopic sensitivity of the yellow field of the pigeon's retina to ultraviolet light.

The photopic spectral sensitivity of the yellow field of the pigeon's retina to UV light was determined electrophysiologically. The sensitivity curve could be approximated with a model in which the activity of only two cone types were incorporated. In this model, the first type of cone had a maximum sensitivity at 366 nm and was combined with an oil droplet that is completely transparent in the UV wavelength range. The second type had a sensitivity maximum at 415 nm and was associated with an oil droplet cutting off light below 390 nm.

The relation between celestial colour gradients and the position of the sun, with regard to the sun compass.

Colour gradients along the sky caused by atmospheric scattering were measured on sunny days. It is concluded that whereas the shape of the spectral intensity distribution in the short wavelength range is stable, the distribution at longer wavelengths depends on the direction of measurement. We expressed these relative intensity differences as a spectral contrast. This contrast plotted as a function of angular difference with respect to the position of the sun establishes a smooth gradient. We suggest that the pigeon's UV sensitivity is part of a colour processing system, which is well adapted to employ these gradients in order to derive the sun's position.

THE ORIENTATION OF THE E-VECTOR OF LINEARLY POLARIZED LIGHT DOES NOT AFFECT THE BEHAVIOUR OF THE PIGEON COLUMBA LIVIA

Orientation with reference to the time-compensated sun-azimuth compass has been established for the homing pigeon Columba livia. Previous qualitative studies claim that pigeons are sensitive to the orientation of a polarizer and it has been suggested that these animals are able to use sky-light polarization as an indirect reference to the sun's position when the latter is shielded from view. We report experiments which were undertaken to quantify the sensitivity of the homing pigeon to the orientation of linearly polarized light. The results of our initial experiments suggested that the animals responded to secondary cues. Further experiments were carried out to avoid such artefacts. Under circumstances where secondary cues were rigorously avoided, we were, however, not able to demonstrate any directional response that was caused by the E-vector orientation of the illumination. These results throw doubt on the suggested polarization-sensitivity of birds in general.

Artificial lighting in poultry houses: do hens perceive the modulation of fluorescent lamps as flicker?

1. Many poultry houses are illuminated by fluorescent lamps which produce discontinuous illumination with a frequency of either 100 or 120 Hz. 2. This study investigated whether domestic fowls perceive this discontinuity as flicker by training two Leghorn hens to choose between a continuous and a discontinuous light, all other variables being identical. 3. The light-stimulus was either monochromatic with 100% sinusoidal modulation or a fluorescent lamp whose modulation frequency could be electrically adjusted. 4. Each (correct) choice for the discontinuous light was followed by a 5 Hz higher frequency, whereas an incorrect choice was followed by a 10 Hz lower frequency. 5. On the basis of this principle the animals themselves established the highest perceivable frequency of the discontinuous light, called the Critical Fusion Frequency (CFF), that they could discriminate from continuous light. 6. These frequencies typically depend on the stimulus intensity increasing with increasing intensities, until a maximum value is reached. 7. Two factors limited the magnitudes of the CFF's that were recorded: the maximum stimulus intensities produced and variability in the chicken's response ("behavioural noise"). In spite of these constraints 105 Hz was established as the maximum CFF. 8. On the basis of extrapolation it is concluded that the direct light from fluorescent lamps driven by 50 Hz alternating current is seen by the chicken as flickering. 9. The results justify large-scale comparison of behaviour and production in poultry houses that are illuminated either by low-frequency or by high-frequency fluorescent lamps.

The spectral sensitivity of blue-sensitive pigeon cones: evidence for complete screening of the visual pigment by the oil-droplets.

The relative spectral sensitivity of blue-sensitive pigeon cones was determined using flicker-photometry based on mass ERG-responses from intact subjects during high-level light adaptation. The resulting spectral sensitivity curve can be mimicked by a P460 nomogram screened by an oil-droplet that absorbs 50% at 466 nm. Comparison of the curve with the nomogram indicates that on the average less than 10% of the light that excites the blue-sensitive cones is guided past or diffracted around their oil-droplets.

Early colour deprivation in a monkey (Macaca fascicularis).

Various forms of selective visual deprivation are known to affect the development of the monkey visual system. In the present study a monkey was born and spent the first three months of its life under red illumination. Despite this colour deprivation, the young monkey learnt to distinguish between colours. Furthermore, the monkeys' increment threshold spectral sensitivity was not affected by the deprivation.

Photopic spectral sensitivities of the red and the yellow field of the pigeon retina.

The spectral sensitivities of the red field and the yellow field in the retina of the homing pigeon (Columba Livia) were determined on the basis of ERG responses. Between 450 and 550 nm the relative spectral sensitivity of the yellow field turned out to be higher than that of the red field. The results are in agreement with spectral sensitivity data, obtained by behavioural threshold procedures.

Early colour deprivation in the pigeon.

When cats and monkeys are deprived of specific stimuli during an early sensitive period the development of their visual system is known to be affected. In pigeons, pattern discrimination learning has been shown to be affected by monocular deprivation [2]. Our study was set up to examine whether colour discrimination learning could be affected by colour deprivation. Young pigeons were reared under restricted colour illumination for at least 3 months after hatching so as to obtain a group bred under red illumination, one bred under blue illumination and a control group. After this period several psychophysical tests were used to test the pigeons' sense of colour. No significant difference was found between the 'deprived' birds and the controls. The spectral sensitivity, determined with the help of the ERG, did not differ for the three groups. We conclude that early colour deprivation does not affect visual development in the pigeon.

Retinoscopy and chromatic aberration.

The origin of the apparent farsightedness as revealed by retinoscopy in smaller eyes was investigated by using monochromatic retinoscopy on wild rabbits. Our results indicate that a combination of long wavelength light and chromatic aberration of the subject's dioptrics is the major source of this artifact.