Psychophysical measurement of temporal modulation sensitivity in the tree shrew (Tupaia belangeri)

Temporal modulation sensitivity functions (MSFs) were measured behaviorally in three adult tree shrews (Tupaia belangeri). Shrews were trained to detect temporal sinusoidally-modulated full-field luminance variations in one of three stimuli, the two alternatives being static stimuli of equal size and time-averaged luminance (34 cd/m2). Modulation depth was varied trial-by-trial using a modified staircase technique under ambient illumination of 16 lux. Threshold modulation depths were determined for five temporal frequencies ranging from 3.7 to 47 Hz. Results revealed temporal MSFs that peaked at 15 Hz with a low-frequency roll-off and an extrapolated high-frequency cut-off beyond 50 Hz. These findings confirm the comparatively good temporal vision of Tupaia predicted by behavioral observations.