Related Experiment Video
Updated: Jun 20, 2026
06:00
Assessment of Spatial Lingual Tactile Sensitivity using a Gratings Orientation Test
Published on: September 17, 2021
Spatial contrast sensitivity and grating acuity of barn owls
Wolf M Harmening1, Petra Nikolay, Julius Orlowski
1Department of Zoology and Animal Physiology, RWTH Aachen, Aachen, Germany. wolf@bio2.rwth-aachen.de
Journal of Vision
|September 19, 2009
Summary
Barn owls have excellent eye optics but surprisingly poor visual perception. Behavioral experiments reveal low contrast sensitivity and grating acuity, suggesting vision is not solely determined by optical quality.
Area of Science:
- Ornithology
- Vision Science
- Animal Behavior
Background:
- Barn owl eyes exhibit minimal aberrations, indicating high optical quality.
- The study investigates if this optical excellence translates to superior visual perception in barn owls.
Purpose of the Study:
- To measure the spatial contrast sensitivity function (CSF) and grating acuity in barn owls.
- To determine if excellent eye optics correlate with high visual performance in this species.
Main Methods:
- Psychophysical techniques were employed to measure visual performance in two barn owls.
- Spatial contrast sensitivity function (CSF) and grating acuity were assessed at a luminance of 2.7 cd/m(2).
Main Results:
- The barn owl CSF showed a typical inverted U-shape with low maximum contrast sensitivity (8-19 at 1 cyc/deg).
- Grating acuity, estimated from the CSF, ranged from 3.0-3.7 cyc/deg, and directly measured acuity was 2.6-4.0 cyc/deg.
- These findings place barn owls at the lower end of visual acuity among birds.
Conclusions:
- Barn owls possess low visual acuity and contrast sensitivity despite excellent eye optics.
- Visual resolution and sensitivity in birds are not solely predictable by optical quality alone.
Related Concept Videos
01:20Anatomy of the Eyeball
The eye is a spherical, hollow structure composed of three tissue layers. The outer layer — the fibrous tunic, comprises the sclera — a white structure — and the cornea, which is transparent. The sclera encompasses some of the ocular surface, most of which is not visible. However, the 'white of the eye' is distinctively visible in humans compared to other species. The cornea, a clear covering at the front of the eye, enables light penetration. The eye's middle layer, the vascular tunic,...
01:15Depth Perception and Spatial Vision
Depth perception is the ability to perceive objects three-dimensionally. It relies on two types of cues: binocular and monocular. Binocular cues depend on the combination of images from both eyes and how the eyes work together. Since the eyes are in slightly different positions, each eye captures a slightly different image. This disparity between images, known as binocular disparity, helps the brain interpret depth. When the brain compares these images, it determines the distance to an object.
01:22Photoreceptors and Visual Pathways
At the molecular level, visual signals trigger transformations in photopigment molecules, resulting in changes in the photoreceptor cell's membrane potential. The photon's energy level is denoted by its wavelength, with each specific wavelength of visible light associated with a distinct color. The spectral range of visible light, classified as electromagnetic radiation, spans from 380 to 720 nm. Electromagnetic radiation wavelengths exceeding 720 nm fall under the infrared category, whereas...