Herbert S. Terrace, director
Click on any of the experiments to see a description:
Linear Configurational Learning Shared Mechanisms of Ordinal Judgement Conditional Spatial Discrimination
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This experiment builds on previous numerical research with nonhuman primates. Our goal was to expand the range of numerosities on which rhesus macaques (Macaca mulatta) have been trained previously and to determine how a monkey represents those values. Results were compared to those of human subjects to compare enumeration mechanisms used on this task. Three primary questions this task addresses are:
Monkeys were presented with stimuli composed of geometric figures that differed in size, shape, and color. Cues including shape, color, element configuration, cumulative surface area, and element density were progressively eliminated to ensure reliance on numerosity rather than secondary cues. Additionally, stimulus elements were heterogeneous in color and shape. The sample was shown in a random location on a blue background. Touching the sample extinguished it, and following a one second delay, the test screen displayed the target and distractors on a green background. Correct responses were followed by a banana-flavored food pellet, a change in the color of the monitor, and a distinct sound. Incorrect responses were followed by a different distinct sound and a 4 second time out during which the screen was dark. Monkeys were tested with two stimulus continua: values 1-9 followed by values 1-15. Human subjects were tested with the same stimulus parameters as those of the monkeys, with the exception of a response time restriction to limit reaction times to the range of monkey reaction times.
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Linear Configurational Learning We know that monkeys are great at learning lists. How they mentally represent those lists is unclear. Previous tasks show distance effects for 2-item subsets derived from one or more lists on which they were trained (D'Amato & Colombo, 1988; Terrace, Son & Brannon, 2003). The general result was that accuracy of responding increased and reaction time decreased as the ordinal distance between the test items increased. Such distance effects suggest that list items were represented spatially along a linear continuum. To investigate this hypothesis, we used monkeys (Macaca mulatta) with experience on the simultaneous chaining paradigm. On the original simultanous chaining paradigm, subjects received primary reinforcement if and only if they had responded, in a particular order, to an array of 4 photographs that were displayed simultaneously on a touch-sensitive video monitor. To insure that subjects couldn’t learn the required sequence as a motor plan, the position of the list items varied randomly from trial to trial. In the current paradigm we used the same procedure with a few modifications. A simultaneous chain was displayed in one of four different configurations: linear (vertical [top to bottom] and horizontal [left to right] where the spatial position matches the list order), probe linear (horizontal or vertical but spatial position does not match order position), and simchain (random spatial position). If subjects represented list items spatially, they might be able to use the hint provided on those trials on which the required sequence could be executed by following a spatial rule. Our results to date show that, on 4-item lists, monkeys benefited from trials on which they could respond to the list in a linear manner. Positive transfer from linear trials to trials on which the spatial location of list items varied randomly support the hypothesis that subjects do indeed organize list items along a spatial continuum. This is the first step in a series of experiments targeted towards determining if presentation of a list with matching spatial and order positioning will increase the rate of acquisition and retention of a serial list.
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Do animals remember who cooperated with them and who competed with them in the past? Anecdotal evidence suggests that his is so. However, any attempt at experimentally determining whether they have this capability has failed to draw conclusive results. This study will enable rhesus macaques to demonstrate this ability in a naturalistic but highly controlled social situation. It is naturalistic in that two macaques will be involved in the social interaction, unlike other studies that have utilized human experimenters as part of the dyad. Experimental control is maintained by minimizing the number of possible responses and having one subject directly influence the outcome of the other. By determining the reward contingency of each trial for of the other monkey, each subject has the opportunity to choose to compete or cooperate with the other.
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Shared Mechanisms of Ordinal Judgment Do monkeys represent all ordinal lists in the same way? In this experiment we investigate whether knowledge acquired using different methods of training can be readily transferred to a different ordinal task. Monkeys are trained on the transitive inference task where they infer the order of a list of pictures through trial and error through the presentation of adjacent pairs. Once they acquire the lists we present all of the pictures from a list simultaneously. For half the lists we will reinforce the same order the monkeys learned during training (the congruent condition), but for the other half we will reinforce a different order (the incongruent condition). We expect that the monkeys will benefit by transitive inference training in the congruent condition because we believe there is an underlying mechanism of ordinal representation shared by both experimental paradigms (simultaneous and pair-wise presentation of stimuli).
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Conditional Spatial Discrimination
The spatial conditioning task investigates whether rhesus macaques can transfer a spatial representation to a sequential representation. Monkeys will be presented with arrays of stimuli (AAAA, BBBB, CCCC, DDDD) in which each stimulus has a predetermined ordinal value. This stimulus presentation is purely spatial, with the position of the target being the only cue regarding the overall sequence order. After training monkeys to respond to the correct spatial position for each stimulus, subjects will be presented with a list containing each stimulus. Of primary interest is whether monkeys can transfer learned spatial positional information to ordinal positional information in the context of list learning.
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The serial probe recognition task is used to examine the characteristics of lists in working memory. Of primary interest is whether results show a Serial Position Effect (SPE), which is characterized by primacy (better memory for items at the beginning of the list) and recency (better memory for items at the end of the list) effects, and comparatively poorer memory for items in the middle of the list. In monkey subjects, memory strength can be measured by both accuracy and reaction time.
During a serial probe recognition trial, the monkey sees a series of sample stimuli (arbitrary pictures), presented successively. Following a delay, the monkey is shown a probe and two icons, a “yes” icon, and a “no” icon. The probe is either one of the sample stimuli just shown, or a novel stimulus. If the stimulus is one of the previously presented stimuli, the monkey should respond by touching the “yes” icon; if it is a novel stimulus, the monkey should respond by touching the “no” icon. Correct responses are followed by a banana-flavored food pellet, a change in the color of the monitor, and a distinct sound. Incorrect responses are followed by a different distinct sound and a time out during which the screen is dark. Our monkeys have worked up to long sample lists and significant delays between sample list presentation and the probe. Results thus far do not indicate a traditional SPE. Accuracy for early list items is poor, accuracy for later list items is good, and accuracy for intermediate list items is intermediate. Thus, in terms of accuracy, monkeys show an effect of recency, but no effect of primacy. For a video clip of Coltrane doing SPR, go to Videos.
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