George Ettlinger

Cross-modal recognition of familiar and unfamiliar objects by the monkey: the effects of ablation of polysensory neocortex or of the amygdaloid complex.

Nine rhesus monkeys were trained to a standard level of cross-modal recognition (CMR) in the directions vision to touch and touch to vision. Their level of performance remained essentially unchanged with unfamiliar objects. Five then received bilateral removals of frontal, temporal and parietal polysensory cortex in one stage or successively, and 4 underwent removal of the amygdaloid complex in one stage. All animals were retrained to criterion with familiar objects and then again tested with unfamiliar objects. Postoperatively, the monkeys with extensive neocortical removals were unimpaired or slightly impaired with familiar objects, and slightly impaired (in only one direction) with unfamiliar objects. The animals with amygdaloid ablations showed a different pattern of change: with familiar objects they were unimpaired (if removals were less extensive), or were severely but transiently impaired (if the removals of the amygdala were more extensive and/or other structures were involved); with unfamiliar objects they were unimpaired, tending to improve. The neocortical polysensory areas may be necessary for generating new visual representations during learning--a performance required only for the CMR of unfamiliar objects.

Intermanual Transfer of Mirror-Image Discrimination by Monkeys:

Mirror image equivalence has been studied in four monkeys during inter-manual transfer of tactile discrimination learning. The tasks were designed to progressively reduce the possibility that discrimination would be based on use of the thumb. On three of the four tasks there were consistently significant mirror reversals. The findings support the supposition that mirror inversion occurs during the formation of memory traces, and specifically when the trace is laid down in a second cerebral hemisphere.

Visually guided reaching and tactile discrimination performance in the monkey: The effects of removals of parietal cortex soon after birth

Unilateral removals of parietal cortex were made soon after birth in 5 monkeys. The inferior parietal lobule was removed alone or together with the superior parietal lobule; the second somatosensory area (SII) was removed alone or together with posterior parietal surface cortex. Neurological changes were observed; and the animals were assessed quantitatively for their accuracy of reaching for visual targets and for their ability to discriminate between objects by palpation in the dark. Each hand was evaluated separately. Disorders of reaching (confined to the contralateral hand) were found to persist longer than in animals with comparable removals made at a later age; whereas the ability to make tactile discriminations was not more severely impaired after an early than a late ablation.

Confusion of Laterally Inverted Mirror-Images: A Relationship to Brain Anatomy?

Whereas in the monkey brain the representation of spatial direction (left/ right) is the same for visual and for tactual inflow, in the human brain visual and tactual lateral directions are not aligned with respect to one another. This anatomical feature of the human brain may account in part for the particular difficulty young sighted children have with laterally inverted forms. A small group of children who were totally blind since birth distinguished mirror pairs by touch significantly more easily than did sighted children of comparable age; and monkeys succeeded at cross-modal recognition of laterally inverted mirror pairs better (relative to control pairs) than did sighted children.

Cross-modal recognition by the monkey: Can the experience in the first modality be reduced to a single trial?

Using the cross-modal recognition procedure previously described, but now progressively reducing the number of learning trials given in the first sense modality, three unselected and unoperated rhesus monkeys (and one with bilateral removals of frontal, temporal and parietal polysensory cortex) were able to maintain an average level of 75% correct cross-modal recognition with only 1-3 learning trials. The pool size seemed less important than the familiarity of the objects. No discontinuity between single-trial and multiple-trial learning procedures was detected. Instead, the number of objects available at one time during learning was regarded as critical for distinguishing between these two kinds of learning procedure.

Differential Accuracy of Aimed Movements to Visual and Somatic Targets in Young Children

Children, aged 2.5-8 years, were required to touch accurately a target located either on their bodies or on the chair in which they sat. Movements were made when visual information was: 1. complete (target lit for 3 s, room illuminated); 2. partial (target lit for 3 s, room dark); 3. reduced (target lit for 0.7 s, room dark); and finally, when the target was somatically specified. Movements to visible targets did not differ in any important way as a function of target location with respect to on/off body. Accuracy improved with age to visually but noto somatically specified targets, decreased with decreasing availability of visual information, and was poorest to somatically specified targets. We conclude that during development, the sense-modality through which the target is specified and the visibility of the arm/hand during the movement, but not the personal/extra personal visible space in which the target is located, are important determinants of reaching performance.

Perceptual Categorization is Associated with Sensory Performance in Patients with Unilateral Cerebral Lesions

In this investigation of perceptual categorization (PC), .right-sided brain-damaged patients (RBD) were not impaired for PC of line drawings of animals relative to left-sided brain-damaged (LBD) patients, contrary to what was expected from previous work. Moreover, in both LBD and RBD patients PC performance was significantly associated with performance on a series of 6 sensory tests. These differed from conventional tests in that successive comparisons were required; and in 2 of the 6 tests gratings were discriminated.

Tactile recognition of laterally inverted mirror images by children: intermanual transfer and rotation of the palm.

Intermanual tactile recognition of laterally inverted mirror shapes was studied, with special reference to the role of the thumb. Children were allowed to feel the shapes either with the whole hand, with only four fingers (excluding the thumb), or with only the index finger. Intramanual recognition was also studied after rotation of the hand from the palm down/up to the palm up/down orientation. The thumb was found not to be important for intermanual mirror reversals, and only of limited importance for intramanual reversals. There was no evidence that coding with reference to the hand is of importance for either inter- or intramanual reversals. The explanations for the two kinds of reversals are quite different.

Tactile Recognition of Mirror Images by Children: Intermanual Transfer and Rotation of the Palm

In order to evaluate the importance of the axis of stimulus presentation, inter- and intramanual recognition of mirror pairs was studied with the stimulus materials aligned along the front/back axis (whereas in previous work the mirror pairs were aligned along the left/right axis). Children were allowed to feel shapes with the whole hand, with only four fingers (excluding the thumb), or with only the index finger. After learning with one hand, recognition was tested in experiment 1 with the other hand; after learning with one orientation of the hand (palm down or up), recognition was tested in experiment 2 with the other orientation (palm up or down) of the same hand; after learning with one coronal alignment of the hand (to the left or right), recognition was tested in experiment 3 with the other alignment (to the right or left), but without rotation, of the same hand. Significantly fewer intermanual recognition errors were made on mirror pairs with the materials oriented along the front/back axis than in previous work when oriented along the left/right axis. This supports the suggestion that such errors arise when the stimuli are oriented along the left/right axis during formation of the memory trace. The same trend was unexpectedly obtained for intramanual recognition errors (after rotation of the hand). These errors (after hand rotation) are largely due to coding with respect to the hand; they are reduced when the hand is not aligned with the body axis, since then coding can also occur in relation to the environment.