Spatial contrast sensitivity and grating acuity of barn owls

Abstract

The eyes of barn owls (Tyto alba pratincola) display very little aberrations, and have thus excellent optical quality. In a series of behavioral experiments, we tested whether this presumably beneficial feature is also reflected at a perceptual level in this species. As fundamental indicators for visual performance, the spatial contrast sensitivity function (CSF) and grating acuity were measured in two barn owls with psychophysical techniques. Stimulus luminance was 2.7 cd/m(2). The CSF found here renders the typical band-limited, inverted U-shaped function, with a low maximum contrast sensitivity of 8-19 at a spatial frequency of 1 cyc/deg. Grating acuity was estimated from the CSF high frequency cut-off and yielded 3.0-3.7 cyc/deg. In a second experiment, in which contrast was held constant and spatial frequency was varied, grating acuity was measured directly (2.6-4.0 cyc/deg). These results put barn owls at the very low end of the visual acuity spectrum of birds, and demonstrate that visual resolution and sensitivity cannot be predicted by optical considerations alone.

Bird colour vision: behavioural thresholds reveal receptor noise

“…The Weber fraction for human LWS cone photoreceptors has been suggested to be 0.018 (Wyszecki and Stiles, 2000), which is much smaller than the Weber fraction for bird LWS cones (0.06 for chickens and 0.1 for Leiothrix and budgerigars). This difference could explain why we found no obvious difference in colour discrimination threshold between humans and birds and may also help to explain why birds generally have lower contrast sensitivity than humans (Ghim and Hodos, 2006;Gover et al, 2009;Harmening et al, 2009;Lind et al, 2012).…”

Comparative neurophysiology of spatial luminance contrast sensitivity.

“…Martin and Gordon (1974) and Harmening et al (2009) used behavioral methods to study the contrast sensitivity of three species of owls (Tyto alba pranticola, Strix aluco, and Bubo virginianos). Harmening et al (2009) found a contrast sensitivity peak of 1-2 cpd and visual acuity of 3-4 cpd. Ghim and Hodos (2006) used pattern electroretinography to compare the CSF of several bird species, including falcons (Falco sparvarius), owls (Tyto alba), European starlings (Sturnus vulgaris), quails (Coturnix coturnix japonica), red-bellied woodpeckers (Melanerpes carolinus), and pigeons (Columbia livia).…”

Dominant Vertical Orientation Processing without Clustered Maps: Early Visual Brain Dynamics Imaged with Voltage-Sensitive Dye in the Pigeon Visual Wulst

“…Its behavioral acuity (12.6 cyc/°) (Hahmann and Güntürkün, 1993) surpasses many mammalian species (Van Hooser and Nelson, 2006) and is even three times higher than the barn owl (Harmening et al, 2009). Against the owl, the pigeon Wulst may be less well differentiated in cytoarchitecture (Karten et al, 1973), receives less afferent input from the GLd, and has neurons with larger receptive fields [4.5° (Miceli et al, 1979) vs 1-2°in owls (Pettigrew, 1979)].…”

“…Particularly, the owl visual Wulst is extensively involved in the interpretation of binocular interaction (Pettigrew and Konishi, 1976;Pettigrew, 1979;Nieder and Wagner, 2001) and additionally performs more complicated functions, such as the representation of illusory contours (Nieder and Wagner, 1999). Despite excellent optics and a well developed visual Wulst, the barn owl's behavioral acuity belongs to the lower end of examined birds (Harmening et al, 2009).…”