Considerations on the use of video playbacks as visual stimuli: the Lisbon workshop consensus

Abstract

This paper is the consensus of a workshop that critically evaluated the utility and problems of video playbacks as stimuli in studies of visual behavior. We suggest that video playback is probably suitable for studying motion, shape, texture, size, and brightness. Studying color is problematic because video systems are specifically designed for humans. Any difference in color perception must lead to a different color sensation in most animals. Another potentially problematic limitation of video images is that they lack depth cues derived from stereopsis, accommodation, and motion parallax. Nonetheless, when used appropriately, video playback allows an unprecedented range of questions in visual communication to be addressed. It is important to note that most of the potential limitations of video playback are not unique to this technique but are relevant to all studies of visual signaling in animals.

Female gray treefrogs, Hyla versicolor, are responsive to visual stimuli but unselective of stimulus characteristics

“…However, we consider this an unlikely explanation for our results because females were clearly able to rapidly detect the rather dim visual stimuli, in contrast to Buchanan's (Buchanan, 1993) finding that some measures of foraging performance were reduced following exposure to red light in the closely related Hyla chrysoscelis. This phototactic response provides significant challenges to the interpretation of video playbacks because even if females exhibit a differential response towards certain stimuli, they may do so for reasons related to general perceptual biases towards video images that do not necessarily share anything in common with the natural features the videos are supposed to represent (Oliveira et al, 2000). An important difficulty with video playbacks is that it is challenging to present the relevant features of a signal to the study species because playback devices are generally designed for the human visual system (D'Eath, 1998;Fleishman and Endler, 2000;Fleishman et al, 1998).…”

“…Video playbacks are a widely used but difficult to implement methodology for the study of animal vision, and we illustrate particular hazards to their use that remain underappreciated, even after many reviews of this methodology (e.g. Oliveira et al, 2000).…”

Quantity discrimination in salamanders

“…Both types of experiments used stimuli on an LCD screen and these lack depth cues derived from stereopsis, accommodation and motion parallax (Oliveira et al, 2000;Zeil, 2000). Salamanders use information from stereopsis and accommodation for prey capture (Roth, 1987;Wiggers et al, 1995).…”

Picture recognition of food by macaques (Macaca silenus)

“…Using photographs, line drawings, slides, and video to represent live animals or natural objects provides an alternative to presenting the real items as stimuli. Using images provides researchers with greater control over the stimuli presented to an animal and allows for repeated exposure of the same stimuli to all subjects in a study (D'Eath 1998;Fagot et al 1999;Oliveira et al 2000;Rosenthal 1999). However, an overriding concern when using images as stimuli rather than the actual items is whether the animals conceptualize the two-dimensional image as the three-dimensional object it is intended to represent (see review by Bovet and Vauclair 2000).…”