INTEROCULAR TRANSFER OF A LUMINOUS DISCRIMINATION IN THE RABBIT
FLUX
GARY P. D~C~ERS~Xand AUSTIS H. RIESEX Department of Psychology. University of California, Riverside. CA 92503. U.S.A. (Rrcriced
i9 fanuar~ 1976; in
rerisedfirm
19 .-lprii 1976)
Abstract-Six normally reared rabbits were trained monocularly on a luminous flux discrimination and tested for interocular transfer. While none of the animals showed complete transfer, all but one required fewer trials to relearn the task with the second eye. The performance of one subject monocularly deprived from birth did not differ from the normals. The results are compared with findings of interocular transfer in other vertebrate species. The visual behavior of the rabbit in its natural habitat as it relates to laboratory tests for interocular transfer is also discussed. INTRODCCTIOK
Most normally reared vertebrates, whether they have both crossed and uncrossed optic fibers or totally crossed fibers. show complete interocular transfer of monocularlv learned visual discrimination habits from the driginally trained eye to the second, untrained eye. Goldfish have been shown to transfer color information learned monocularly (Ingle, 1965: McCleary. 1960). and pigeons are able to transfer both color and shape information if the stimuli are presented in an appropriate area of the bird’s visual field (Levine, 19Jj). Mammals have a partial decussation of the optic pathways at the optic chiasm. Lashley (1924) presented evidence for interocular transfer of a brightness discr~ination in the albino rat and Sheridan (1965) showed that hooded rats transfer both brightness and pattern discriminations. Normally reared cats show complete and immediate interocular transfer of both flux and pattern discriminations and monocularly deprived cats. although not able to show perfect transfer on these tasks, display considerable savings when using the second eye (Riesen, Kurke and Mellinger, 1953). Kittens dark-reared for 16 weeks from birth, however, show immediate and complete interocular transfer of a visual flux discrimination (Aarons. Halasz and Riesen. 1963). Cats with both the optic chiasm and corpus cailosum sectioned also transfer a flux discrimination but not a pattern discrimination (Meikle and Sechzer, 1960). The rabbit is a ground-d~veIIing, common prey mamma1 with reiativelv few uncrossed retinal fibers. Normally reared rabbits have been conditioned to discriminate horizontal and vertical lines and lines of different oblique orientations (Van Hof, 1966), but were unable to transfer these tasks (Van Hof, 1970). Chow and Spear (1974) monocularly deprived rabbits from birth by means of lid suturing. The animals were monocularly conditioned on a simultaneous luminous flux discrimination at about 3 months and then tested for interocular transfer. No rabbit showed complete transfer of the task; however, each rabbit learned the task faster with the second eye than with the first. This finding suggests that normaIIy reared rabbits might show immediate interocular transfer of this type of discrimination.
The following experiment was designed to test for interocular transfer of a luminous flux discrimination in normally reared rabbits. Although the rabbit has relativeIy few uncrossed optic fibers, like the albino rat, it was hypothesized that the rabbit would show
complete interocular transfer since the rat shows this ability. METHODS Six normal and one monocularly deprived, healthy, adult-female Dutch-belted rabbits with pigmented eyes served as the subjects in the experiment. The deprived subject was born in the laboratory and 10 days after birth, before the eyes opened. the right ey-elid was sutured to prevent patterned light stimulation. This animal was returned to the mother until weaning at 2 months of age. This animal entered the experimental procedure at approx 5 months of age. A two-choice discrimination box adapted from Zilbert and Riesen (t971) and very much like that used by Van Hof (1966) was used in the experiment and will be only briefly described here. Two 10.2cm square openings 6.4 cm apart were cut out of one wall. Each opening could be covered from the rear by a translucent Plexiglas baclcwardswinging hinged door. The hinged stimulus doors, 12 x 12 cm muares of translucent Plexizlas (Rohm & Hass Co., w-2447),‘one of which was pain&t flat black, could be blocked or pushed open to give access to a food tray located behind each door, The stimulus doors were illuminated from behind by four 24-V d.c. aviation-type bulbs mounted 30 cm away. Both food trays were always baited to prevent any differential olfactory cues. Training and testing took place in a dark. sound attenuated room. Each animal was brought to SOY/,of its ad ~~b~rurn weight’ with water available only in the home cages. Each time an animal was placed in the apparatus, it was first fitted with a naugahyde hood which covered one eye. The animals had normal binocular vision at all other times. The hoods were constructed with a thin leather strap which ran under the jaw and was buckled behind the ears, preventing any light from entering the covered eye. The eye chosen for original training was determined randomly. After the anin& obtained ?ood’reinforcement (two 0.2.g pellets of Purina Rabbit Chow). the animal was trained io push each stimulus door op& to obtain food. After all position preferences were eliminated, training was started. The positive light and negative dark stimuli were positioned on each trial using a modified Gellerman (1933) series which allowed no more than three successive placements of the stimuli in the same position. Ten trials
GLRL. P.
16
Drc~~aso~ and .\~STIN Ei. Rns~s
were given each day with an intertrial interval of 3Osec. A noncorr~tion procedure was used with an error being scored if the rabbit pushed its bead against the dark negative stimulus in an attempt to gain reinforcement. Performance of 90% correct or better on two successive days was the criterion for learning the task. The day after an animal reached this criterion with the first eye, it was fitted with a second naugahydr hood which now covered the first eye and allowed vision with the second. The animal was then tested for interocular transfer. RESULTS The animals displayed little obvious visually guided
behavior in their home cages before the experiment and appeared tense and rigid when first picked up for hand&g. AI1 animafs adapted we11to the pretraining procedure, however, and readily Ieamed to push open the stimulus doors. None of the animals displayed any difliculty eating while wearing the hoods. The cornea of the monocularly deprived subject (rabbit 7) was clear when the deprived eye was opened and no opacities developed through the conclusion of the experiment. Although this animal received monocular visual deprivation from birth, her training and testing scores were well within the range of the scores of the other subjects. This animal’s scores are grouped with the data obtained from the other six subjects. Table I shows the number of training sessions required by each animal to reach criterion with both the first and the second ey-e. All animals but one required fewer trials to reach criterion using the second eye than using the tirst eye (P = 0.055, onetailed binomial test); however, no animal showed immediate and complete interocular transfer. Figure 1 shows the learning curves for two rabbits; the one showing the highest savings score (rabbit 2), and the one showing the smallest savings (rabbit 5). Although rabbit 5 required 15 sessions with the second eye, after iive sessions this animal was consis-
Table 1. The number of training sessions required to rsach
criterion with the first and the second zl;e by monocularly trained rabbits an a Ruu discrrmination Subject ‘IL) 3Rj 4Ri 5(L) 7(L)? 9(L) 10(R) iMeans kf rdians
Sessions I0 criterion* First eye Second eye 16 1.4 13 10 12 13 ‘6 i-1.8 I3
_i : 10 15 It 11 9.1 I@
O0savings with second eye 69”. 50”” , .,I -J ,i -500, W’, iY,, 33”o 3-70.I 50”2
* Probab~ity = O.Ojj. + Monocularly deprived from birth. tentlv performing at 709; correct or better for the remaining 10 sessions. This is significantly above chance. DlSCLSSlOiV
The resuhs of the present experiment indicate that five of six normally reared rabbits, when trained monocularly on a Iuminous flux discrimination. exhibited a signifkant amount of savings when tested for interocular transfer. The 507; median savings (Table 1) is far from the nearly l#o/, savings observed in cats (Riesen et al., 19533, indicating that the transfer was neither immediate nor complete. These results are consistent with a previous report of the absence of interocular transfer of line orientation discriminations in normally reared rabbits (Van Hof, 1966) and with previous reports of savings during interocular transfer of a luminous flux discrimination in rabbits reared monocularly from birth (Chow and Spear, 1979. The present results suggest that within the
I
-RABBIT C-4
I RA331T
2
65
t
S
ESSIONS
Fig. 1. Monocular discrimination performance of two rabbits on a luminous liuv task. Left: original learning with first eye; Right: transfer and relearning with second eye.
21
Interocular transfer in the rabbit paradigm employed. the normally reared rabbit’s inability to show complete interocular transfer of line orientation discriminations may be extended to in-
clude a gross flux discrimination as well. Extensive pretraining experience given each animal prior to the start of the experiment mitigates against a possible interpretation of transfer as being due to mere familiarization with the apparatus. Performance above 5@; in initial tests with the second eye (Fig. 1) suggests that the relevant stimuli had some control over the response. Ocular equivalence may not be complete in any species, including man. For most purposes, and barring certain well-known anomalous conditions such as amblyopia, we presume a high degree of equivalence for human vision. If a competitive task is used to put ocular &quivalence to a severe test, even the normal cat reveals some lack of transfer (Schissler and Riesen, 1969). With common training and testing procedures, the normally reared cat does show immediate transfer of a luminous flux discrimination (Aarons rt al.. 1963). The normally reared rabbit, on the other hand, placed in the same experimental paradigm, from the results of the present experiment, shows a slight savings with the second eye on a monocularly learned flux discrimination. The data presently available suggest a difference between the rabbit and most other vertebrate species on the ability for interocular transfer. In addition, Van Sluyters and Stewart (1974) found the neurons in the binocular area of the rabbit brain to be bi-ocular, that is, having nonidentical receptive fields on the two retinae, rather than binocular, like visual cortex neurons in the cat. However, binocularity alone is not a necessary condition for interocular transfer. The goldfish, a bi-ocular vertebrate with exclusively contralateral retinal projections, has been shown to transfer visual discriminations interocularly (Ingle, 1965; McCleary, 1960). Pigeons also are bi-ocular vertebrates with totally contralateral retinal projections. Levine (1945) found that pigeons show interocular transfer of both color and form if the stimuli are presented in front of and below the bird’s head. When the stimuli are presented directly in front of the bird, no interocular transfer is observed. While eye placement and the amount of binocular interaction are important factors that must be considered in a discussion of interocular transfer, the different cues present in a visual stimulus and where these cues are located in the visual field are equally important. Perhaps the use of moving stimuli placed on the horizon would yield a more species-meaningful analysis of interocular transfer in the rabbit. Empirical data are needed to test this possibility.
.4cknowledqements-The
authors thank Dr. David L. Stewart for his suggestions and encouragement throughout the experiment. We thank Ms. Helen Neely for her assistance. This research was supported by PHS Grant EYOO573 to A. H. Riesen and by NIMH Traineeship MH 11291 to G. P. Dickerson.
REFEREXCES
Aarons L., Halasz H. K. and Riesen A. H. (1963) Interocular transfer of visual intensity discrimination after ablation of striate cortex in dark-reared kittens. J. camp. ph_vsiol. Psychol. 56, 196-199. Chow K. L. and Soear P. D. (1974) Moroholoeical and functional effects’ of visual deprivation ‘on &e rabbit visual system. EXp/ .Veurol. -12. -129117. Gellerman L. W. (1933) Chance orders of alternating stimuli in visual discrimination experiments. J. genet. PsJchol.
42, 206-208.
Ingle D. J. (1965) Interocular transfer in goldfish: color easier than pattern. Science 149, ICOO-lC?C.
Lashlev K. S. (192-1)Studies of cerebral function in learning. ‘VI. The’ theory that synaptic resistance is reduced’ by the passage of the nerve impulse. Psycho/. Ret,. 31. 369-375. Levine J. (1945) Studies in the interrelations of central nervous structures in binocular vision. II. The conditions under which interocular transfer of discriminative habits takes place in the pigeon. J. gene?. Psychol. 67, 131-l-12. McCleary R. A. (1960) Type of response as a factor in interocular transfer in the fish. J. camp. physiol. Psycho/. 53. 311-321. Meikle T. H. and Sechzer J. A. (1960) Interocular transfer of brightness discrimination in “split-brain” cats. Science 132. i3t735 Riesen A. H., Kurke M. I. and Mellinger J. C. (1953) Interocular transfer of habits learned monocularly in visually naive and visually experienced cats. J. camp. phpiol. Psycho/. 46, 166-171.
Schissler D. R. and Riesen A. H. (1969) Partial interocular transfer of visual discriminations in cats. Decel. Psychobiol. 2. 81-86. Sheridan C. L. (1965) Interocular transfer of brightness and pattern discriminations in normal and corpus callosumsectioned rats. J. camp. physioi. Psychol. 59, 292-29-l. Stewart D. L. and Dickerson G. P. (1975) Interocular transfer and visual cliff performance following monocular deprivation in the rabbit. Van Hof M. W. (1966) Discrimination between striated patterns of different orientation in the rabbit. Vision Res. b. 89-9-1. Van Hof M. W. (1970) Interocuiar transfer in the rabbit. &I .Vncrol. 26, 103-108. Van ‘Sluyrers R. C. and Stewart D. L. (197-r) Binocular neurons of the rabbit’s visual cortex: receptive field characteristics. E.~pl Brain Rrs. 19, 166195. Zilbert D. E. and Riesen A. H. (1971) A comparison of the effects of infant and adult retinal lesions upon visual acuity in the rabbit. Espl Neural. 33, 44i-l58.
FLUX
GARY P. D~C~ERS~Xand AUSTIS H. RIESEX Department of Psychology. University of California, Riverside. CA 92503. U.S.A. (Rrcriced
i9 fanuar~ 1976; in
rerisedfirm
19 .-lprii 1976)
Abstract-Six normally reared rabbits were trained monocularly on a luminous flux discrimination and tested for interocular transfer. While none of the animals showed complete transfer, all but one required fewer trials to relearn the task with the second eye. The performance of one subject monocularly deprived from birth did not differ from the normals. The results are compared with findings of interocular transfer in other vertebrate species. The visual behavior of the rabbit in its natural habitat as it relates to laboratory tests for interocular transfer is also discussed. INTRODCCTIOK
Most normally reared vertebrates, whether they have both crossed and uncrossed optic fibers or totally crossed fibers. show complete interocular transfer of monocularlv learned visual discrimination habits from the driginally trained eye to the second, untrained eye. Goldfish have been shown to transfer color information learned monocularly (Ingle, 1965: McCleary. 1960). and pigeons are able to transfer both color and shape information if the stimuli are presented in an appropriate area of the bird’s visual field (Levine, 19Jj). Mammals have a partial decussation of the optic pathways at the optic chiasm. Lashley (1924) presented evidence for interocular transfer of a brightness discr~ination in the albino rat and Sheridan (1965) showed that hooded rats transfer both brightness and pattern discriminations. Normally reared cats show complete and immediate interocular transfer of both flux and pattern discriminations and monocularly deprived cats. although not able to show perfect transfer on these tasks, display considerable savings when using the second eye (Riesen, Kurke and Mellinger, 1953). Kittens dark-reared for 16 weeks from birth, however, show immediate and complete interocular transfer of a visual flux discrimination (Aarons. Halasz and Riesen. 1963). Cats with both the optic chiasm and corpus cailosum sectioned also transfer a flux discrimination but not a pattern discrimination (Meikle and Sechzer, 1960). The rabbit is a ground-d~veIIing, common prey mamma1 with reiativelv few uncrossed retinal fibers. Normally reared rabbits have been conditioned to discriminate horizontal and vertical lines and lines of different oblique orientations (Van Hof, 1966), but were unable to transfer these tasks (Van Hof, 1970). Chow and Spear (1974) monocularly deprived rabbits from birth by means of lid suturing. The animals were monocularly conditioned on a simultaneous luminous flux discrimination at about 3 months and then tested for interocular transfer. No rabbit showed complete transfer of the task; however, each rabbit learned the task faster with the second eye than with the first. This finding suggests that normaIIy reared rabbits might show immediate interocular transfer of this type of discrimination.
The following experiment was designed to test for interocular transfer of a luminous flux discrimination in normally reared rabbits. Although the rabbit has relativeIy few uncrossed optic fibers, like the albino rat, it was hypothesized that the rabbit would show
complete interocular transfer since the rat shows this ability. METHODS Six normal and one monocularly deprived, healthy, adult-female Dutch-belted rabbits with pigmented eyes served as the subjects in the experiment. The deprived subject was born in the laboratory and 10 days after birth, before the eyes opened. the right ey-elid was sutured to prevent patterned light stimulation. This animal was returned to the mother until weaning at 2 months of age. This animal entered the experimental procedure at approx 5 months of age. A two-choice discrimination box adapted from Zilbert and Riesen (t971) and very much like that used by Van Hof (1966) was used in the experiment and will be only briefly described here. Two 10.2cm square openings 6.4 cm apart were cut out of one wall. Each opening could be covered from the rear by a translucent Plexiglas baclcwardswinging hinged door. The hinged stimulus doors, 12 x 12 cm muares of translucent Plexizlas (Rohm & Hass Co., w-2447),‘one of which was pain&t flat black, could be blocked or pushed open to give access to a food tray located behind each door, The stimulus doors were illuminated from behind by four 24-V d.c. aviation-type bulbs mounted 30 cm away. Both food trays were always baited to prevent any differential olfactory cues. Training and testing took place in a dark. sound attenuated room. Each animal was brought to SOY/,of its ad ~~b~rurn weight’ with water available only in the home cages. Each time an animal was placed in the apparatus, it was first fitted with a naugahyde hood which covered one eye. The animals had normal binocular vision at all other times. The hoods were constructed with a thin leather strap which ran under the jaw and was buckled behind the ears, preventing any light from entering the covered eye. The eye chosen for original training was determined randomly. After the anin& obtained ?ood’reinforcement (two 0.2.g pellets of Purina Rabbit Chow). the animal was trained io push each stimulus door op& to obtain food. After all position preferences were eliminated, training was started. The positive light and negative dark stimuli were positioned on each trial using a modified Gellerman (1933) series which allowed no more than three successive placements of the stimuli in the same position. Ten trials
GLRL. P.
16
Drc~~aso~ and .\~STIN Ei. Rns~s
were given each day with an intertrial interval of 3Osec. A noncorr~tion procedure was used with an error being scored if the rabbit pushed its bead against the dark negative stimulus in an attempt to gain reinforcement. Performance of 90% correct or better on two successive days was the criterion for learning the task. The day after an animal reached this criterion with the first eye, it was fitted with a second naugahydr hood which now covered the first eye and allowed vision with the second. The animal was then tested for interocular transfer. RESULTS The animals displayed little obvious visually guided
behavior in their home cages before the experiment and appeared tense and rigid when first picked up for hand&g. AI1 animafs adapted we11to the pretraining procedure, however, and readily Ieamed to push open the stimulus doors. None of the animals displayed any difliculty eating while wearing the hoods. The cornea of the monocularly deprived subject (rabbit 7) was clear when the deprived eye was opened and no opacities developed through the conclusion of the experiment. Although this animal received monocular visual deprivation from birth, her training and testing scores were well within the range of the scores of the other subjects. This animal’s scores are grouped with the data obtained from the other six subjects. Table I shows the number of training sessions required by each animal to reach criterion with both the first and the second ey-e. All animals but one required fewer trials to reach criterion using the second eye than using the tirst eye (P = 0.055, onetailed binomial test); however, no animal showed immediate and complete interocular transfer. Figure 1 shows the learning curves for two rabbits; the one showing the highest savings score (rabbit 2), and the one showing the smallest savings (rabbit 5). Although rabbit 5 required 15 sessions with the second eye, after iive sessions this animal was consis-
Table 1. The number of training sessions required to rsach
criterion with the first and the second zl;e by monocularly trained rabbits an a Ruu discrrmination Subject ‘IL) 3Rj 4Ri 5(L) 7(L)? 9(L) 10(R) iMeans kf rdians
Sessions I0 criterion* First eye Second eye 16 1.4 13 10 12 13 ‘6 i-1.8 I3
_i : 10 15 It 11 9.1 I@
O0savings with second eye 69”. 50”” , .,I -J ,i -500, W’, iY,, 33”o 3-70.I 50”2
* Probab~ity = O.Ojj. + Monocularly deprived from birth. tentlv performing at 709; correct or better for the remaining 10 sessions. This is significantly above chance. DlSCLSSlOiV
The resuhs of the present experiment indicate that five of six normally reared rabbits, when trained monocularly on a Iuminous flux discrimination. exhibited a signifkant amount of savings when tested for interocular transfer. The 507; median savings (Table 1) is far from the nearly l#o/, savings observed in cats (Riesen et al., 19533, indicating that the transfer was neither immediate nor complete. These results are consistent with a previous report of the absence of interocular transfer of line orientation discriminations in normally reared rabbits (Van Hof, 1966) and with previous reports of savings during interocular transfer of a luminous flux discrimination in rabbits reared monocularly from birth (Chow and Spear, 1979. The present results suggest that within the
I
-RABBIT C-4
I RA331T
2
65
t
S
ESSIONS
Fig. 1. Monocular discrimination performance of two rabbits on a luminous liuv task. Left: original learning with first eye; Right: transfer and relearning with second eye.
21
Interocular transfer in the rabbit paradigm employed. the normally reared rabbit’s inability to show complete interocular transfer of line orientation discriminations may be extended to in-
clude a gross flux discrimination as well. Extensive pretraining experience given each animal prior to the start of the experiment mitigates against a possible interpretation of transfer as being due to mere familiarization with the apparatus. Performance above 5@; in initial tests with the second eye (Fig. 1) suggests that the relevant stimuli had some control over the response. Ocular equivalence may not be complete in any species, including man. For most purposes, and barring certain well-known anomalous conditions such as amblyopia, we presume a high degree of equivalence for human vision. If a competitive task is used to put ocular &quivalence to a severe test, even the normal cat reveals some lack of transfer (Schissler and Riesen, 1969). With common training and testing procedures, the normally reared cat does show immediate transfer of a luminous flux discrimination (Aarons rt al.. 1963). The normally reared rabbit, on the other hand, placed in the same experimental paradigm, from the results of the present experiment, shows a slight savings with the second eye on a monocularly learned flux discrimination. The data presently available suggest a difference between the rabbit and most other vertebrate species on the ability for interocular transfer. In addition, Van Sluyters and Stewart (1974) found the neurons in the binocular area of the rabbit brain to be bi-ocular, that is, having nonidentical receptive fields on the two retinae, rather than binocular, like visual cortex neurons in the cat. However, binocularity alone is not a necessary condition for interocular transfer. The goldfish, a bi-ocular vertebrate with exclusively contralateral retinal projections, has been shown to transfer visual discriminations interocularly (Ingle, 1965; McCleary, 1960). Pigeons also are bi-ocular vertebrates with totally contralateral retinal projections. Levine (1945) found that pigeons show interocular transfer of both color and form if the stimuli are presented in front of and below the bird’s head. When the stimuli are presented directly in front of the bird, no interocular transfer is observed. While eye placement and the amount of binocular interaction are important factors that must be considered in a discussion of interocular transfer, the different cues present in a visual stimulus and where these cues are located in the visual field are equally important. Perhaps the use of moving stimuli placed on the horizon would yield a more species-meaningful analysis of interocular transfer in the rabbit. Empirical data are needed to test this possibility.
.4cknowledqements-The
authors thank Dr. David L. Stewart for his suggestions and encouragement throughout the experiment. We thank Ms. Helen Neely for her assistance. This research was supported by PHS Grant EYOO573 to A. H. Riesen and by NIMH Traineeship MH 11291 to G. P. Dickerson.
REFEREXCES
Aarons L., Halasz H. K. and Riesen A. H. (1963) Interocular transfer of visual intensity discrimination after ablation of striate cortex in dark-reared kittens. J. camp. ph_vsiol. Psychol. 56, 196-199. Chow K. L. and Soear P. D. (1974) Moroholoeical and functional effects’ of visual deprivation ‘on &e rabbit visual system. EXp/ .Veurol. -12. -129117. Gellerman L. W. (1933) Chance orders of alternating stimuli in visual discrimination experiments. J. genet. PsJchol.
42, 206-208.
Ingle D. J. (1965) Interocular transfer in goldfish: color easier than pattern. Science 149, ICOO-lC?C.
Lashlev K. S. (192-1)Studies of cerebral function in learning. ‘VI. The’ theory that synaptic resistance is reduced’ by the passage of the nerve impulse. Psycho/. Ret,. 31. 369-375. Levine J. (1945) Studies in the interrelations of central nervous structures in binocular vision. II. The conditions under which interocular transfer of discriminative habits takes place in the pigeon. J. gene?. Psychol. 67, 131-l-12. McCleary R. A. (1960) Type of response as a factor in interocular transfer in the fish. J. camp. physiol. Psycho/. 53. 311-321. Meikle T. H. and Sechzer J. A. (1960) Interocular transfer of brightness discrimination in “split-brain” cats. Science 132. i3t735 Riesen A. H., Kurke M. I. and Mellinger J. C. (1953) Interocular transfer of habits learned monocularly in visually naive and visually experienced cats. J. camp. phpiol. Psycho/. 46, 166-171.
Schissler D. R. and Riesen A. H. (1969) Partial interocular transfer of visual discriminations in cats. Decel. Psychobiol. 2. 81-86. Sheridan C. L. (1965) Interocular transfer of brightness and pattern discriminations in normal and corpus callosumsectioned rats. J. camp. physioi. Psychol. 59, 292-29-l. Stewart D. L. and Dickerson G. P. (1975) Interocular transfer and visual cliff performance following monocular deprivation in the rabbit. Van Hof M. W. (1966) Discrimination between striated patterns of different orientation in the rabbit. Vision Res. b. 89-9-1. Van Hof M. W. (1970) Interocuiar transfer in the rabbit. &I .Vncrol. 26, 103-108. Van ‘Sluyrers R. C. and Stewart D. L. (197-r) Binocular neurons of the rabbit’s visual cortex: receptive field characteristics. E.~pl Brain Rrs. 19, 166195. Zilbert D. E. and Riesen A. H. (1971) A comparison of the effects of infant and adult retinal lesions upon visual acuity in the rabbit. Espl Neural. 33, 44i-l58.
