Integration of form and motion in the anterior superior temporal polysensory area (STPa) of the macaque monkey

1. Processing of visual information in primates is believed to occur in at least two separate cortical pathways, commonly labeled the "form" and "motion" pathways. This division lies in marked contrast to our everyday visual experience, in which we have a unified percept of both the form and motion of objects, implying integration of both types of information. We report here on a neuronal population in the anterior part of the superior temporal polysensory area (STPa) both sensitive to form (heads and bodies) and selective for motion direction. 2. A total of 161 cells were found to be sensitive to body form and motion. The majority of cells (125 of 161, 78%) responded to only one combination of view and direction (termed unimodal cells, e.g., left profile view moving left, not right profile moving left, or left profile moving right). We show that the response of some of these cells is selective for both the motion and the form of a single object, not simply the juxtaposition of appropriate form and motion signals. 3. A smaller number of cells (9 of 161, 6%) responded selectively to two opposite combinations of view and direction (e.g., left profile moving left and right profile moving right, but no other view and direction combinations). A few cells (4 of 161, 2%) showed "object-centered" selectivity to view and direction combinations, responding to all directions of motion where the body moves in a direction compatible with the direction it faces, for example, responding to left profile going left, right profile going right, face view moving toward the observer, back view moving away from the observer, but not other view and direction combinations. 4. The majority of the neurons (106 of 138, 77%) selective for specific body view and direction combinations responded best to compatible motion (e.g., left profile moving left), and one fourth (23%) showed selectivity for incompatible motion (e.g., right profile moving left). 5. The relative strengths of motion and form inputs to cells in STPa conjointly sensitive to information about form and motion were assessed. The majority of the responses (95%) were characterized as showing nonlinear summation of form and motion inputs. 6. The capacity to discriminate different directions and different forms was compared across three populations of STPa cells, namely those sensitive to 1) form only, 2) motion only, and 3) both form and motion. The selectivity of the latter class could be predicted from combinations of the other two classes. 7. The response latencies of cells selective for form and motion are on average coincident with cells selective for direction of motion (but not stimulus form). Both these cell populations have response latencies on average 20 ms earlier than cells selective for static form. 8. Calculation of the average of early response latency cells (cell whose response latency was under the sample mean) suggests that direction information is present in cell responses some 35 ms before form information becomes evident. Direction information and form information become evident within 5 ms of each other in the average late response latency cells (those cells whose response latency was greater than the sample mean). Inputs relating to movement show an initial response period that does not discriminate direction. The quality of initial direction discrimination appeared to be independent of response latency. The initial discrimination of form was related to response latency in that cells with longer response latencies showed greater initial discrimination of form in their responses. We argue that these findings are consistent with form inputs arriving to area STPa approximately 20 ms after motion inputs into area STPa.

Short-Term Retention of “Surprising” Events by Pigeons

Terry and Wagner (1975) have suggested that the short-term retention of information about an event is enhanced if the occurrence of the event is made unexpected or surprising. Three experiments tested this idea using delayed conditional position (Experiment I) and colour discriminations (Experiments II and III). The subjects were pigeons and the presentation of food was the target event to be remembered. Choice of one of two simultaneously presented stimuli was reinforced if the retention interval had been initiated by presentation of target food. Contrary to Terry and Wagner's claim, retention was superior on probe test trials in Experiments I and II if the presentation of the target food was preceded by a previously established signal for food (CS+) rather than by a stimulus which had not been paired with food (CS-). Experiment III systematically manipulated the signalling conditions used during initial discrimination training. Retention was better following a CS+ presentation if the target food had been signalled during initial discrimination training but worse if the food presentation had been unsignalled. These results do not favour the idea that retention of an event is directly affected by whether or not the target event is surprising.

Accuracy of Imitative Production and Discrimination: Effects of Contingent Feedback

The effect of contingent vs noncontingent feedback on accuracy of imitative production of 8 Polish words was examined for 7 males and 7 females at a rural day care center. In addition, a second measure, on which discrimination of correct and incorrect forms of the same Polish words was required, was administered before and after production training. Accuracy of production improved over sessions for the group receiving contingent feedback; accuracy of production in the noncontingent feedback group did not improve. Both groups performed at chance level during the initial discrimination test and improved significantly and nondifferentially on the later test. The results are discussed in terms of their implications for language development and imitation.

The Effect of Task Difficulty and Criteria of Learning on a Subsequent Reversal

Two experiments using rats were carried out in which it was shown that a quadratic function can best describe the relation between amount of initial discrimination training and speed of reversal learning for both a difficult visual and an easy spatial task. The results are used to explain the rarity of the over learning reversal effect (ORE) using easy tasks such as position discriminations. Implications for the attention theory are also discussed.