THE OPTOMOTOR RESPONSE: A LOW-TECH TOOL TO DETERMINE VISUAL PROPERTIES
Optomotor responses are based on the innate tendency to stabilize a moving image on the retina and are widely spread among animals from varies classes (Land, 1999). The responses are elicited by the visual perception of a horizontally moving pattern of contrasting vertical lines (Jellali et al., 2005; Muntz, 1974; Davis, 1972), whereby the eyes, head and entire body follow the moving pattern or whereby the eyes show optokinetic nystagmus (repeatedly following the movement direction of the pattern at about the same speed and then snap back in the opposite direction; Fritsches and Marshall, 2002).
Invertebrates with light-sensitive organs do not always show motion detection required for optomotor response. Instead, non-predating gastropods and annelids, bivalve molluscs and primitive arthropods lacking a lobula complex, may have a shadow response, i.e. a protective response to a dimming of the ambient light which signals as the approach of a potential predator (Land & Nilsson, 2006). Still, many animals with a well-developed uninjured visual system are capable to show some sort of optokinetic response, suggesting its adaptive significance both for orientation and visual acuity (Walls, 1942). Using the optomotor apparatus described elsewhere on this website, optomotor response was poorly evoked at a flicker frequency of 2,2 cycles/s in a small rodent (Muridae; personal observations). Better results were obtained with locusts (Acrididae) and goldfish (Ciprinidae; personal observations). In a similar experiment no optomotor response was observed in earth-worms (Lumbricidae; personal observations).
Independent behavioural responses to horizontal and vertical components of a given movement stimulus are likely to be necessary attributes in flying insects and birds and in pelagic swimming fish, and these responses were indeed demonstrated in flying insects (Saleem et al., 2012; Götz, 1969). They appear to serve stabilization of orientation during free locomotion with respect to the visible environment and they are probably related to movement detection of either the subject or object (Strauss et al., 2001; Lehrer, 1993; Coombe, 1984).
The optomotor response (OMR) may also be a trigger stimulus for synchronized and coordinated movements, which are characteristic of flocking and schooling behaviour (Imada et al., 2010). Schooling – and probably flocking as well – is non-hierarchical ( i.e.no individual dominates another) and its adaptive significance is largely understood as an anti-predator defence in fish (Pitcher, 1986). Schooling and flocking in vertebrates as well as swarming and tracking in insects can be interpreted as an adaptive spin-off behaviour of the original visual demands on movement fixation.
The OMR behavioural paradigm has been used to measure varies aspects of the visual system in a range of animals (Wallman, 1975). Today, optokinetic responses are used in studies related to medicines and economics, like induced visual dysfunction (e.g. Redfern et al., 2011; Cachafeiro et al., 2010; Douglas et al., 2010), the influence of neuropharmaca (Rihel & Schier, 2011; Mora-Ferrer & Neumeyer, 2008), commercial fishing (Arimoto et al., 2010)and commercial aquaculture (Herbert et al., 2011). OMR may also be used in the support of eco-evolutionary theories, like the sensitivity hypothesis (Robinson et al., 2011)and the sensory drive hypothesis (Maan & Seehausen, 2010) and it may conduce to a better understanding of alien visual properties (Cummings, 2008). Above all, it remains a low budget and easy to handle tool to measure visual thresholds, like motion detection (Kim & Jung, 2010), contrast sensitivity (Umino et al., 2008) and colour vision with respect to sexual selection (Rick et al., 2011) or short wave (UV) sensitivity (Nava et al., 2011). Recent applications to study the occurrence of polarization sensitivity have been carried out in cephalopods and cuttlefish (Talbot & Marshall, 2010; Horváth & Kriska, 2008). In the near future it will also be used to extend the investigations on polarization sensitivity in fish (elsewhere on this site).
The relative simplicity of the set-up and the redundancy to inflict physical injury of the experimental animals deserve to be considered next to the precise question and available equipment.
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