Purchase this article with an account.
Heywood M. Petry, Chelsea Clark, Jonathan Day-Brown, R.T. Bolin, Martha Bickford; Behavioral measurement of RDK velocity discrimination thresholds in the tree shrew.. Journal of Vision 2012;12(9):1223. doi: 10.1167/12.9.1223.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Tree shrews are fast-moving diurnal mammals with cone-dominated retinas and well-developed visual systems. They are considered to be a prototype of early primates. Often the subject of anatomical, physiological and imaging studies, behavioral assessment of their visual capabilities is limited. Previously we reported psychophysical measurements of spatial CSF (Petry et al., 1984); color vision (Petry & Kelly, 1991) and temporal vision (Callahan & Petry, 2000). Here we report psychophysical assessment of velocity discrimination thresholds. Two adult tree shrews (Tupaia belangeri ) were trained in an operant chamber on a 3-alternative forced-choice task to detect a velocity difference in one of three stimuli (an "odd-ball" task). The stimuli were computer generated random dot kinematograms (RDKs; Vision Research Graphics) consisting of white dots on a black background (dot size 3x2 pixels). Each stimulus subtended 25.5deg visual angle when viewed at 15.5cm. A response was registered when the animal touched the stimulus. Correct responses were rewarded with fruit juice. Foil RDKs drifted at 90deg at 5 deg/sec. The oddball also drifted at 90deg, but at a higher velocity, starting at 15 deg/sec. Velocity of the oddball was varied trial-by-trial using a modified staircase technique. Frequency-of-seeing curves were calculated with threshold performance defined as midway between maximum performance and chance (see above references for more detail on the analysis). Results revealed Weber fractions of 1.0 and 0.9 for the two shrews. These values were about 1 log unit poorer than for human observers tested using the same apparatus, but were closer to values reported for cats (e.g., under roughly comparable conditions, Lomber et al., 2010 found fractions of about 0.5). Given the much smaller eye size and array of retinal neurons of tree shrews, their comparatively good velocity discrimination likely provides a necessary survival capacity related to their own fast movements and to those of their prey.
Meeting abstract presented at VSS 2012
This PDF is available to Subscribers Only