Research reportGlobal motion detection is impaired in cats deprived early of pattern vision
Introduction
There are many different kinds of motion stimuli that provide input to the visual system (see [16], [21]). Among these, global motion stimuli are most commonly used in motion perception tests in both humans and animals. Such stimuli are usually produced using moving random patterns, textures, gratings and apparent dot displacements. During global motion the subject is unable to extract an individual picture element from the overall pattern and to follow its route. Thus, global motion is presumably perceived by the visual system due to the integration of the small picture elements over a large portion of the visual field and carries only information about pure motion, without any additional spatial cues.
Pasternak and her colleagues studied the effects of early motion deprivation in strobe-reared cats on the global motion perception. Despite having substantially reduced numbers of directionally selective cells in several visual structures (see, e.g. [32]), those cats were only slightly impaired in global direction discrimination tasks and only when tested at threshold [22], [24], [26].
On the other hand, the effects of early pattern deprivation in motion perception have been examined using only relative motion stimuli. In the relative motion the changes in the position of a stimulus with respect to spatial cues (the edges of the screen, walls of the training apparatus, etc.) can be helpful in perception. We examined relative motion perception in cats binocularly deprived of pattern vision by mask-rearing in the early period of life (binocularly deprived cats (BD cats)). Vertical and horizontal oscillations of a light spot [45] and constant downward or upward movement [2] were used. In the first study [45], the learning was difficult even for undeprived control cats (C cats) and somewhat more difficult for the BD cats. In the following study [2] the oscillations were replaced by a linear movement to enhance the unidirectional motion stimulation, which probably evokes stronger cell responses within the visual cortex (see [8]). The BD cats could only detect the moving stimulus from the stationary stimulus, whereas the C cats were able to discriminate between opposite directions of movement.
To eliminate the influence of positional cues in motion task, in the present study, we investigated global motion detection. A moving random-dot pattern versus a stationary random dot pattern was used in BD cats and C cats. For a comparison, relative motion detection tasks were also given.
Section snippets
Subjects
Two BD cats and four C undeprived cats were used. The BD cats were deprived of the pattern visual experience by means of double-thickness linen masks covering their eyes. The masks were put on before the eyelids opened and were removed at 6 months of age. This procedure reduces retinal lumination to a degree similar to lid suturing [11] but is less traumatic. The C and BD cats were reared together in large home cages (3×2.6×2.35 m), where they were allowed to play and interact freely. The
Velocity 7° per s
The positive stimulus was a moving random-dot pattern and the negative consisted of the same pattern but stationary. The task appeared to be very difficult for both the C and BD cats. All cats performed at chance during the entire training period of 25 sessions. The mean of percentage of correct responses during the last five sessions in cats C1, C2, C3, C4, BD5 and BD6 was, respectively, 63, 59, 52, 48, 53 and 50.
To make the distinction between the stimuli more pronounced, the fading-in
Discussion
We have found that cats binocularly deprived of pattern input in the early period of life suffer severe impairment in the detection of global motion with velocity of 50° per s in comparison with C cats. This is in contrast to the only minor deficits found in the detection of relative motion in BD cats in the previous studies [2], [45] and no difference in performance between the C and BD cats in the simple relative motion detection task found in this study. This discrepancy between the previous
Acknowledgements
We thank Krystyna Dec and Wioletta Waleszczyk for comments, Steve Raiguel for linguistic help, Aleksander Nowinski for programming and Irena Łapinska for technical help. This work was supported by a Polish-Flemish grant BIL 99/29.
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