Testing Visual Sensitivity to the Speed and Direction of Motion in Lizards

Summary

Testing visual sensitivity in lizards using an operant conditioning paradigm that employs video playback of random-dot kinematograms and computer-generated invertebrates.

Abstract

Testing visual sensitivity in any species provides basic information regarding behaviour, evolution, and ecology. However, testing specific features of the visual system provide more empirical evidence for functional applications. Investigation into the sensory system provides information about the sensory capacity, learning and memory ability, and establishes known baseline behaviour in which to gauge deviations (Burghardt, 1977). However, unlike mammalian or avian systems, testing for learning and memory in a reptile species is difficult. Furthermore, using an operant paradigm as a psychophysical measure of sensory ability is likewise as difficult. Historically, reptilian species have responded poorly to conditioning trials because of issues related to motivation, physiology, metabolism, and basic biological characteristics. Here, I demonstrate an operant paradigm used a novel model lizard species, the Jacky dragon (Amphibolurus muricatus) and describe how to test peripheral sensitivity to salient speed and motion characteristics. This method uses an innovative approach to assessing learning and sensory capacity in lizards. I employ the use of random-dot kinematograms (RDKs) to measure sensitivity to speed, and manipulate the level of signal strength by changing the proportion of dots moving in a coherent direction. RDKs do not represent a biologically meaningful stimulus, engages the visual system, and is a classic psychophysical tool used to measure sensitivity in humans and other animals. Here, RDKs are displayed to lizards using three video playback systems. Lizards are to select the direction (left or right) in which they perceive dots to be moving. Selection of the appropriate direction is reinforced by biologically important prey stimuli, simulated by computer-animated invertebrates.

Protocol

Jacky Dragons Jacky lizards (A. muricatus) were held in climate-controlled captive facilities. Enclosures were constructed of fabricated glass terrariums measuring 60 cm3. Enclosures were also filled with Sydney sand substrate, native foliage, and natural wooden perches. Enclosures were placed on top of movable trolleys that allowed for subjects to be placed in the middle of all viewing m…

Discussion

Testing the sensory capacity in lizard species has been difficult, and has largely been both a tedious and arduous process. These difficulties stem from finding the correct reinforcer or establishing a functional protocol. Here, I established a successful protocol in which to test motion perception in lizards. This procedure may also be applicable in testing other visual characteristics as well as other sensory mechanisms. In addition, this procedure may be applicable to other species. The usefulness of this protocol no…

Materials

Material Name	Type	Company	Catalogue Number	Comment
iMac	Computer	Apple Computers, Inc.		Three systems
Canopus®	Digital-to-analog converter	Canopus®	ADVC110
Sony Trintron	Colour viewfinder	Sony Corporation	PVM-14M2A, PVM-14L2, PVM-14N5A	Three monitors
Canon	Digital camcorder	Cannon Inc.	MV650i	Records behavior
NEC	Colour viewfinder	NEC	1892	View responses
Sony VCR	VHS recorder	Sony Corporation	SLV-EZ717AS	Record behavior to VHS
VHS tape			Generic VHS	Recording media
VPixx	Software program	VPixx Technologies, Inc.	v1.79	To create RDKs
Final Cut Pro	Software program	Apple Computer, Inc.	HD	To create playback sequences
Lightwave® 3D	Software program	NewTek Inc.	v8.3	To create secondary reinforcers
Mealworm	Tenebrio molitor	Pisces Enterprises LTD		Primary reinforcer
Cricket	Achetus domesticus	Pisces Enterprises LTD		Food for husbandry
Terrariums	Glass	Crystal Palace Aquariums		Enclosure material for lizards (60 x 60 x 60 cm)
Globes	Spotone	Phillips		125W, Heat lamps for lizards
Ultraviolet globes	Ultra-Vitalux	Osram		300W, UV lamps for lizards
Herptivite		Rep-Cal Research Labs		Vitamins: beta carotene, calcium, and vitamin D3