A wavelength discrimination function for the hummingbirdArchilochus alexandri

Summary Free-flying black-chinned hummingbirds (Archilochus alexandri) at a site in southeastern Arizona were attracted to artificial feeders displaying narrow spectral bands of light (7 nm half band width). The birds were taught to discriminate between pairs of wavelengths of approximately equal brightness but with a spectral separation of 10 nm. After training, performance of the birds was not significantly changed by alterations in the relative intensities of the two lights. Moreover, when the spectral composition of the test and training lights was made identical, the birds did not learn to make a discrimination on the basis of intensity differences of 0.5 or 1 log unit. In the learned foraging behavior of these hummingbirds, the salience of brightness is therefore inconsequential relative to hue.Discrimination scores for a constant 10 nm separation of test and training wavelengths were determined between 410 and 650 nm. This measure of the spectral dependence of wavelength discrimination shows a deterioration of performance at the red end of the spectrum but not in the blue and violet. Moreover, the minima at 585 and 555 nm indicate more structure than is present in this region of the spectrum in the human hue discrimination curve, and are similar but not identical to data on pigeon. These results are consistent with a growing body of evidence suggesting that the color space of birds may be more than three dimensional.This work was supported by NIH grants EY03266 and EY00222. We are indebted to Sally and Walter Spofford, who generously allowed us to work at their home, Aguila-Rancho, during May and June of 1980, and without whose kind help these experiments could not have been performed.     

Photorefractoriness in European starlings: associated hypothalamic changes and the involvement of thyroid hormones and prolactin

Responsivity to photostimulation in previously photorefractory European starlings is caused by subjection to short daylengths and is characterized by a marked activation of the hypothalamus in terms of synthesis of gonadotropin releasing hormone. This active hypothalamic state is amplified for a time by a subsequent exposure to long days but is soon completely reversed as the birds become photorefractory again. This latter effect of long photoperiods and the concurrent secretion of prolactin are dependent on the presence of thyroid hormones. Conceivably, prolactin causes photorefractoriness by inhibition at a hypothalamic level.     

Microspectrophotometry of rhodopsin and metarhodopsin in the moth Galleria

Fresh, frozen sections of the photoreceptor layer of the compound eye of the moth Galleria have been examined by microspectrophotometry, using 4 X 8 mum measuring beams that sampled from approximately two to four rhabdoms. The principal visual pigmen: absorbs maximally at 510 nm (P510), and on irradiation is converted to a thermally stable, pH-insensitive metarhodopsin with lambdamax at 484 nm (M484) and a 43% increase in molar extinction coefficient. Subsequently, short wavelength irradiation of the metarhodopsin photoregenerates some P510; but the absence of an isosbestic point in the cycle of spectral changes is consistent with the presence of smaller amounts of violet- or ultraviolet-sensitive visual pigment(s) that also are converted to a blue-absorb g metarhodopsin. Difference spectra for both P510 and M484 were measured, using hydroxylamine. The 484-nm metarhodopsin is reversibly converted to a form with lambdamax at 363 nm by high concentrations of glycerol. Dark regeneration of rhodopsin in vivo after several minutes exposure of thoroughly dark-adapted animals to full sunlight requires several days.     

Experimental cavitation studies in a model head-neck system

The response of two different fluid-filled head-neck models to impact was studied experimentally to provide information concerning the validity of the widely prevalent cavitation hypothesis of brain damage. The structures consisted of an acrylic spherical shell with an outside diameter of about 188 mm and a human calvarium with a clear polyester resin occiput, representing the head, each coupled to an articulated artificial viscoelastic neck. Transient phenomena were initiated by the impact of either cylindrical projectiles fired from a pneumatic gun or by the pendulum drop of an aluminum spherical shell onto a small truncated aluminum cone attached to the head models. A short strain-gaged aluminum cylinder served to measure the input force history, while the pressure in the brain-simulating fluid was ascertained by means of Z-cut tourmaline crystals located along the impact axis at the coup, center and contrecoup positions. The occipital regions of the models were photographed at framing rates of 4000–8000 s⁻¹ to visually examine the cavitation phenomena.

Coup, contrecoup and resonating cavitation were detected and found to coincide temporally with negative pressure transients in both head-neck models. These results lend some support to the cavitation theory as a possible mechanism for brain damage.