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Visual Sensitivity to Orientation of Rectangles in Mice with Retinal Degeneration SAMUEL B. SCHNITZER Department of Psychology Indiana State University Terre Haute, Indiana MILLARD E. N. BEANE Department of Psychology University of New Brunswick Fredericton, New Brunswick Canada
C3H/HeJ male mice, an inbred strain showing retinal degeneration (rd), and normal-eyed DBA/lJ male mice were studied in a task requiring discrimination of horizontally and vertically oriented rectangles. T h e apparatus was a modified Yerkes discrimination apparatus. The mice were given 30 days of discrimination training, 10 trials/day, after which I 0 more trials were given on thc 31st day with positive and negative cues reversed. Both strains showed a highly significant decrease in errors during acquisition, the rd strain making significantly fewcr errors than the DBA/lJ animals. Reversal of the cues brought about a sharp increase in percentage of errors.
A number of inbred mouse strains show an inherited retinal degeneration (Sidman & Green, 1965). The eye develops more or less normally until approximately the 10th postnatal day after which the retina undergoes a progressive degeneration. The external layers are affected first. By about 20 days of age little remains of the photoreceptors and by 9 weeks of age no trace of such cells can be found (Karli, 1952). The internal layers of the retina may retain a relatively normal appearance for some months afterward. Much recent evidence suggests that, in spite of the loss of the photoreceptors, mice afflicted with retinal degeneration (rd) can differentiate visually among varying brightness levels (e.g., Karli, 1952, 1954a; Nagy & Misanin, 1970). Even more surprising are reports of visual response to the orientation of forms. Karli (1954a, b, c), on the basis of 2 studies involving multiple conditions, concluded that rd mice could successfully discriminate between backlighted vertical and horizontal, but otherwise identical, rectangular slits. In 2 out of 3 experiments in which solid forms were
Received for publication 8 August 1974 Revised for publication 7 May 1975 Developmen'tal Psychobiology, 9(2): 167-174 (197 6) 0 1 9 7 6 by John Wiley & Sons, Inc.
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utilized, Bovet-Nitti (1969) obtained results that supported Karli’s findings and extended the reported cababilities of rd mice t o discrimination of IJ-shaped forms lying on their sides with tlie open portions facing in opposite directions. Most of tlie orientation studies, however, reveal possible deficiencies in control and design even when positive results were reported. Karli (19S4a, b ) recognized that the data of his 1st investigation, in which the mice passed through the rectangular slits, indicated at best a preponderant role for vision in the solution of the problem posed. Although willing t o ascribe her results t o visual capacity on the part of her rd mice, Bovet-Nitti (1969) did not make mention of any special efforts t o control for nonvisual cues. Only in the case of Karli’s (1954a, c) 2nd study, in which the mice were required t o push through doors consisting of cellophane packets containing the stimuli, were controls for nonvisual cues even approaching adequacy apparently incorporated. Keinforcing his conclusion that the rd condition does not preclude visual discrimination of the orientation of forms, Karli found that after bilateral enucleation rd mice no longer showed the previously learned discriminatory response. Although this 2nd investigation by Karli seems t o provide convincing evidence for at least one type of form vision in rd mice, and even implicates the deficient retina in the response, it too appears to suffer some inadequacies. For example, some desirable controls, such as for reinforcer odors, were not reported. In most of the cited studies, including Karli’s (19S4a, c) 2nd, problems of research design, aside froni control per se, make difficult certainty that tlie discrimination reported could have been learned only on the basis of vision. For example, the vertical rectangle was apparently always the positive stimulus in Karli’s (1954a) work. If extraneous variables were always associated with particular rectangular orientat ion, learning could presumably have been mediated through such cues rather than by use of the visual aspects of the situation. Even the reported loss of discrimination after bilateral enucleation (which seems t o provide an ultimately convincing argument) proves difficult t o evaluate as Karli did not test control animals, such as sham-operated mice, nor was the time interval between operation and renewed behavioral testing made clear. Given the remarkable nature of the reported findings and the reservations advanced, we felt that further testing for visual orientation would be useful. The present study, based o n Karli’s (1954a, b , c) work, involved an attempt to replicate earlier positive results while using controls that were clearly adequate.
Method Subjects Mice (Mus n~uscuhw)of 3 inbred strains were studied. Eight C3H/HeJ inale mice, a strain afflicted with rti (Sidman & Green, 1965), served as the experimental subjects. Eight normal-eyed DBA/l J male mice (Sidman 81 Green, 1065) were also tested. The latter strain has been reported (Thompson, 1953) similar t o C3H mice, a strain related to C3H/HeJ, in hunger drive and emotionality. All animals were obtained from the Jackson Laboratory, Bar Harbor, Maine, and were housed initially in individual cages in ;I colony room. One week prior t o experimentation the mice were placcd. still
VISUAL SENSITIVITY IN RD MICE
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individually housed, in the experimental room. They were fed and watered ad libitum until the start of training. At the beginning of experimentation the subjects were 65 3 days old.
*
Apparatus The apparatus was similar to that used by Karli (1952), which was itself an adaptation of the Yerkes discrimination apparatus. (See Fig. 1). At the anterior end of the apparatus were 2 start compartments (S, S') each of which opened onto a common area (C) after the raising of the guillotine doors (E, E'). Off C were 2 discrimination chambers (D, D'). Shock grids, which could be operated independently by means of silent switches (Sw, S'w) and through which .3-mA shock could be delivered, consituted the first 15 cm of the chamber floors. At the distal end of D and D' were openings ( 0 , O ' ) 8.5 x 10.5 cm in size. A horizontally sliding carriage, operated by an handle (H), contained 3 equally spaced windows (W, W', W") each the size of 0 and 0'. Any 2 of the windows could be made to coincide with the openings. The windows were fitted with frosted glass behind which were placed black cardboard in which rectangular slits were cut. The rectangles, which were either in horizontal or vertical orientation, measured 5 x 1.6 cm and were centered in the windows. If the horizontal and vertical rectangles had been superimposed, they would have formed a cross, the bottom of the cross being at the base of the window approximately 2.5 cm from the floor. General Electric Reflector flood lamps (120V, 15OW) were placed behind the windows at L and L'. The light passed through the rectangular slits and was adjusted by means of a variable
I
Fig. 1. Top view of the apparatus.
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transformer (Powerstat) t o provide 5000 lux illumination immediately in front of the windows. Temperature readings taken at various locations with a laboratory thermometer indicated n o differences in heat distribution in the 2 halves of the apparatus correlated with the visual stimuli in the windows. Near the windows were 8-cm square entrances (T, T’) to return alleys (A, A’) that led back t o S and S‘. Bottle caps (R, R’), into which the water reinforcement was placed, were nailed t o the floors of A and A’ just anterior t o T and T’. Open bottles (B, B’) filled with water were placed outside the apparatus at positions approximating the caps in order t o provide water vapor in the vicinity of both caps at all times. After the animals had returned t o S or S’, retracing was prevented by the lowering Qf guillotine doors ((3, C’). The apparatus, which was 14 cm deep and uncovered, was made
Visual Sensitivity to Orientation of Rectangles in Mice with Retinal Degeneration SAMUEL B. SCHNITZER Department of Psychology Indiana State University Terre Haute, Indiana MILLARD E. N. BEANE Department of Psychology University of New Brunswick Fredericton, New Brunswick Canada
C3H/HeJ male mice, an inbred strain showing retinal degeneration (rd), and normal-eyed DBA/lJ male mice were studied in a task requiring discrimination of horizontally and vertically oriented rectangles. T h e apparatus was a modified Yerkes discrimination apparatus. The mice were given 30 days of discrimination training, 10 trials/day, after which I 0 more trials were given on thc 31st day with positive and negative cues reversed. Both strains showed a highly significant decrease in errors during acquisition, the rd strain making significantly fewcr errors than the DBA/lJ animals. Reversal of the cues brought about a sharp increase in percentage of errors.
A number of inbred mouse strains show an inherited retinal degeneration (Sidman & Green, 1965). The eye develops more or less normally until approximately the 10th postnatal day after which the retina undergoes a progressive degeneration. The external layers are affected first. By about 20 days of age little remains of the photoreceptors and by 9 weeks of age no trace of such cells can be found (Karli, 1952). The internal layers of the retina may retain a relatively normal appearance for some months afterward. Much recent evidence suggests that, in spite of the loss of the photoreceptors, mice afflicted with retinal degeneration (rd) can differentiate visually among varying brightness levels (e.g., Karli, 1952, 1954a; Nagy & Misanin, 1970). Even more surprising are reports of visual response to the orientation of forms. Karli (1954a, b, c), on the basis of 2 studies involving multiple conditions, concluded that rd mice could successfully discriminate between backlighted vertical and horizontal, but otherwise identical, rectangular slits. In 2 out of 3 experiments in which solid forms were
Received for publication 8 August 1974 Revised for publication 7 May 1975 Developmen'tal Psychobiology, 9(2): 167-174 (197 6) 0 1 9 7 6 by John Wiley & Sons, Inc.
167
168
SCHNlTZER AND BEANE
utilized, Bovet-Nitti (1969) obtained results that supported Karli’s findings and extended the reported cababilities of rd mice t o discrimination of IJ-shaped forms lying on their sides with tlie open portions facing in opposite directions. Most of tlie orientation studies, however, reveal possible deficiencies in control and design even when positive results were reported. Karli (19S4a, b ) recognized that the data of his 1st investigation, in which the mice passed through the rectangular slits, indicated at best a preponderant role for vision in the solution of the problem posed. Although willing t o ascribe her results t o visual capacity on the part of her rd mice, Bovet-Nitti (1969) did not make mention of any special efforts t o control for nonvisual cues. Only in the case of Karli’s (1954a, c) 2nd study, in which the mice were required t o push through doors consisting of cellophane packets containing the stimuli, were controls for nonvisual cues even approaching adequacy apparently incorporated. Keinforcing his conclusion that the rd condition does not preclude visual discrimination of the orientation of forms, Karli found that after bilateral enucleation rd mice no longer showed the previously learned discriminatory response. Although this 2nd investigation by Karli seems t o provide convincing evidence for at least one type of form vision in rd mice, and even implicates the deficient retina in the response, it too appears to suffer some inadequacies. For example, some desirable controls, such as for reinforcer odors, were not reported. In most of the cited studies, including Karli’s (19S4a, c) 2nd, problems of research design, aside froni control per se, make difficult certainty that tlie discrimination reported could have been learned only on the basis of vision. For example, the vertical rectangle was apparently always the positive stimulus in Karli’s (1954a) work. If extraneous variables were always associated with particular rectangular orientat ion, learning could presumably have been mediated through such cues rather than by use of the visual aspects of the situation. Even the reported loss of discrimination after bilateral enucleation (which seems t o provide an ultimately convincing argument) proves difficult t o evaluate as Karli did not test control animals, such as sham-operated mice, nor was the time interval between operation and renewed behavioral testing made clear. Given the remarkable nature of the reported findings and the reservations advanced, we felt that further testing for visual orientation would be useful. The present study, based o n Karli’s (1954a, b , c) work, involved an attempt to replicate earlier positive results while using controls that were clearly adequate.
Method Subjects Mice (Mus n~uscuhw)of 3 inbred strains were studied. Eight C3H/HeJ inale mice, a strain afflicted with rti (Sidman & Green, 1965), served as the experimental subjects. Eight normal-eyed DBA/l J male mice (Sidman 81 Green, 1065) were also tested. The latter strain has been reported (Thompson, 1953) similar t o C3H mice, a strain related to C3H/HeJ, in hunger drive and emotionality. All animals were obtained from the Jackson Laboratory, Bar Harbor, Maine, and were housed initially in individual cages in ;I colony room. One week prior t o experimentation the mice were placcd. still
VISUAL SENSITIVITY IN RD MICE
169
individually housed, in the experimental room. They were fed and watered ad libitum until the start of training. At the beginning of experimentation the subjects were 65 3 days old.
*
Apparatus The apparatus was similar to that used by Karli (1952), which was itself an adaptation of the Yerkes discrimination apparatus. (See Fig. 1). At the anterior end of the apparatus were 2 start compartments (S, S') each of which opened onto a common area (C) after the raising of the guillotine doors (E, E'). Off C were 2 discrimination chambers (D, D'). Shock grids, which could be operated independently by means of silent switches (Sw, S'w) and through which .3-mA shock could be delivered, consituted the first 15 cm of the chamber floors. At the distal end of D and D' were openings ( 0 , O ' ) 8.5 x 10.5 cm in size. A horizontally sliding carriage, operated by an handle (H), contained 3 equally spaced windows (W, W', W") each the size of 0 and 0'. Any 2 of the windows could be made to coincide with the openings. The windows were fitted with frosted glass behind which were placed black cardboard in which rectangular slits were cut. The rectangles, which were either in horizontal or vertical orientation, measured 5 x 1.6 cm and were centered in the windows. If the horizontal and vertical rectangles had been superimposed, they would have formed a cross, the bottom of the cross being at the base of the window approximately 2.5 cm from the floor. General Electric Reflector flood lamps (120V, 15OW) were placed behind the windows at L and L'. The light passed through the rectangular slits and was adjusted by means of a variable
I
Fig. 1. Top view of the apparatus.
170
SCHNITZER AND BEANE
transformer (Powerstat) t o provide 5000 lux illumination immediately in front of the windows. Temperature readings taken at various locations with a laboratory thermometer indicated n o differences in heat distribution in the 2 halves of the apparatus correlated with the visual stimuli in the windows. Near the windows were 8-cm square entrances (T, T’) to return alleys (A, A’) that led back t o S and S‘. Bottle caps (R, R’), into which the water reinforcement was placed, were nailed t o the floors of A and A’ just anterior t o T and T’. Open bottles (B, B’) filled with water were placed outside the apparatus at positions approximating the caps in order t o provide water vapor in the vicinity of both caps at all times. After the animals had returned t o S or S’, retracing was prevented by the lowering Qf guillotine doors ((3, C’). The apparatus, which was 14 cm deep and uncovered, was made
