General

Studying behavioural responses of animals in experimental conditions, ethologists have found relatively simple stimuli that could be more effective than the natural objects. Single spots (called also eye-spots) and two horizontally arranged spots, rectangular longitudinal stripes, periodic gratings and other stimuli (Fig.1) belong to them. Because the foregoing stimuli are not exact imitations of the natural objects, we will call them amimetic stimuli. In several articles, we will group the main visual amimetic stimuli and describe how they are used in the ethological research, whether they occur in the nature as well as their application in the fishing lure industry.

In the framework of applied ethology, we will address to the fishing lure industry. It is that only sphere of the human activites, where artificial stimuli and models of the various animals are used in the largest scale.

Figure 1. The basic visual amimetic stimuli

Names of the basic visual amimetic stimuli used in this article:

Note, stimuli 05 and 06 are periodic spatial, whereas stimuli 07, 08, 09, 10, 11, and 12 are periodic spatiotemporal

In the terminology of early ethologists, some of the amimetic stimuli shown above called the sign stimuli (e.g., Manning & Dawkins, 1998). Generally, using simple stimuli and changing parts of complex stimuli, scientists were able to find the so called supernormal stimuli that induced in animals the more strong behavioural responses than the modelling natural objects.

For example, the giant cane toads, Bufo marinus, respond to the horizontally moving rectangular longitudinal stripes (20 mm long x 2.5 mm high) much more actively (on average of 10 times) than to live crickets and insect plastic models (Robins & Rogers, 2004). Similarly, reproductive males of the common toad, Bufo bufo, prefer (in four cases against one) to form sexual pairs (Fig.2) with the fixed blue discs (5 cm diameter) than with the live mobile females (Gnyubkin & Kondrashev, 1978).

Figure 2. Reproductive males of toads prefer to congregate sexual pairs with blue discs than with live females

Manning and Dawkins (1998) give many other examples of this kind.

Neuroethology

Visual amimetic stimuli induce numerous behavioural responses in many animals and do not imitate, as mentioned above, the concrete natural objects. The effectiveness of these stimuli is grounded on the common mechanisms of visual perception, common for all visually guided animals. Among visual amimetic stimuli, the nature of spots, stripes and gratings, both static and moving, as well as rotating striped drums is most studied.

For example, in fish and other vertebrate animals, spots are detected at the level of ganglion cells of retina, which have the more or less distinct concentric receptive fields with the antagonistic center and periphery. According to Horn (1962; see Fig. 6.5 b,c), the boundaries of some spot are distinguished depending on its size by one or several ganglion cells with the foregoing receptive fields. Rectangular stripes and periodic gratings appeared in the field of view are detected by the so called orientation selective ganglion cells (e.g., Damjanović et. al., 2009). It is shown in numerous electrophysiological tests that the cells of this type are represented by two relatively distinct units called, respectively, the detectors of horizontal lines and the detectors of vertical lines.

In addition, on an example of developing larval zebrafish, Brachydanio (Danio) rerio, as an usable model object, neuromotor grounds of the behavioural responses to artificial and natural visual stimuli are studied, in the larva development (for review, see Portugues & Engert, 2009):

1) responses to large-filed moving vertical gratings, called optomotor responses

2) responses to live parameciums and small moving spots, called prey tracking

3) responses to large moving spots and other large objects, called escape responses

Among other mechanisms of adjusted effectiveness of amimetic visual stimuli matched with the corresponding receptive fields, bilateral symmetry of spots and spatial symmetry of gratings play an exceptionally inportant role (e.g., Kenward et al., 2004). The effectiveness of pair stimuli is determined by the bilateral symmetry of visual system and visual perception evolving during millions of years in the field of the Earth gravitation, but the causes of the evolution of repetitive stilmuli and the corresponding receptive fields are unclear. Kenward et al. (2004) consider about ten factors that might lead to the evolution of repetitive visual stimuli and the corresponding receptive fields, including the highest detectableness of repetitive stimuli on the background of environmental optic noises.

In addition to spatial amimetic visual stimuli, there are more complex spatiotemporal amimetic visual stimuli (for review, see, e.g., Rothental, 2007). In fish, responses to such spatiotemporal stimuli as rhythmic (temporal symmetric) pulsations, vibrations and (worm-like) undulations are innate. In contrast to the spatial periodic gratings (Damjanović et al., 2009), there are not distinct receptive units to detect these complex stimuli.

Basic References

Damjanović I., Maximova E.M., Maximov V.V. 2009. On the organization of receptive fields of orientation-selective units recorded in the fish tectum. Journal of Integrative Neuroscience 8, 323–344

Gnyubkin V.F., Kondrashev C.L. 1978. Pair aggregation in the common toad, Bufo bufo L., in the reproductive period. In: Mechanisms of animal vision. Moscow, Science, 40-75

Horn G. 1962. Some neural correlates of perception. Viewpoints in Biology. Butterworth & Co. Publishers, London, p. 240-285

Kenward B., Wachtmeister C. A., Ghirlanda S., Enquist M. 2004. Spots and stripes: the evolution of repetition in visual signal form. Journal of Theoretical Biology 230, 407-419

Manning A., Dawkins M.S. 1998. An introduction to animal behaviour. 5th editon. UK, Camdridge University Press

Portugues R., Engert F. 2009. The neural basis of visual behaviors in the larval zebrafish. Current Opinion in Neurobiology 19, 1–4

Robins A., Rogers L.J. 2004. Lateralized prey-catching responses in the cane toad, Bufo marinus: analysis of complex visual stimuli. Animal Behaviour 68, 567-575

Rothental G.G. 2007. Spatiotemporal dimensions of visual signals in animal communication. Annual Review of Ecology, Evolution and Systematics 38, 155–78