Herbert S. Terrace, director
Click on any of the experiments to see a description:
Metacognition: Matching to Sample
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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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In an experiment closely related to Numerical Matching to Sample (above), we have been training two monkeys on another Matching to Sample (MTS) paradigm wherein they learn through trial and error to associate numerosity with the corresponding Arabic numeral. Once the training is complete, we will test the subjects to see if the Arabic numerals have not just taken on the discrete numerical value but have also taken on the corresponding ordinal properties.
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How far ahead do monkeys plan when they are executing a Simultaneous Chaining (simchain) list? To determine how many steps ahead the monkeys think, we began this two-part experiment in early 2009. Four monkeys were trained on a five-item simchain list, wherein they had to learn to respond to pictures A, B, C, D, and E in the correct order on every trial, despite the pictures appearing in different locations on the screen on each trial. We then began the first phase of testing. During probe trials, the physical position on the screen of two pictures shifted after a correct response to A, so, for example, C suddenly appeared where B used to be and vice versa. We believed that if we saw consistent errors to C on the second item, i.e., to the location where B used to be, that would show evidence of planning ahead. Indeed, that is what we found. As a counterpart to this shifting paradigm, we have begun to test planning ahead with the help of a masking paradigm. Here, after a correct response to A, the remaining items are covered with a grey mask and the monkey must complete the list in the correct order without being able to see the items. As the items are touched in the correct order, they are unmasked. Responses to items out of sequence end the trial.
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Metacognition: Matching to Sample with 3 Risk Choices The ability to make judgments on one's own knowledge is called metacognition, and for a long time was thought to be a uniquely human ability. In this experiment, we're not just looking for evidence of metacognition in monkeys but for the ability to appropriately choose the level of confidence they have in their judgments. Two monkeys have a history of succeeding in metacognition experiments and have since learned to distinguish three icons that relate to three levels of risk: low, medium, and high. In order that they may lose as well as receive rewards, they have a token hopper on the side of the screen that starts out with some tokens. When they receive enough tokens, they receive banana flavoured pellets.
The paradigm on which they are being tested is Matching to Sample (MTS), with varying numbers of distractors on both the sample and test screens. By increasing the number of distractors, we can make a trial more difficult. Blinking lines around the sample indicate that it's the correct picture and, as in other MTS tasks, during test the monkey must choose the same picture. Currently the monkeys are being tested on a retrospective paradigm, which means they make their confidence judgments after they have chosen the target picture. They choose from one of the three icons to indicate their level of confidence - essentially "betting" on how well they think they did - and are rewarded or punished accordingly. If they bet high and are correct, they win several tokens; if they bet high and are incorrect, they lose several tokens (and thus the opportunity for a pellet). If they choose the medium risk icon, they will win or lose a smaller number of pellets. If they bet low, they receive a pellet whether they're right or wrong. We hypothesize that when there are fewer distractors and therefore the test is easier, they will choose the high risk icon more often because they will be more likely to gain several pellets. Likewise we expect them to choose low or medium risk more often when there are more distractors and the test is harder. |
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If you know that Bert is taller than Ernie who is taller than Elmo, you can infer that Bert is taller than Elmo. This type of logical reasoning is called transitive inference (TI). Based on that idea, we've been testing three monkeys on a TI paradigm that uses relationships between arbitrary pictures in training and testing. On a seven-item list of pictures, ABCDEFG, A comes before B which comes before C and so on. During training, the monkey sees two pictures at a time only, and these pictures are next to each other (adjacent) in the list. Through trial and error, the monkey learns which picture comes first in each pair. During testing, once again the monkey sees only two pictures at a time, but now the pairs can be either adjacent (e.g., A and B) or non-adjacent (e.g., A and D). They monkeys have had success in learning the relationships between non-adjacent pairs on lists up to seven items in lenght. We are examining the data for evidence of symbolic magnitude and distance effects to help us learn more about how these relationships are represented in the mind. We are also looking at how this information transfers to a Simultaneous Chaining (simchain) paradigm for five-item lists. If a monkey has only ever seen elements of a five-item list two at a time in a TI experiment, will that ordinal information transfer successfully when the money is presented with all five items at once? By comparing rate of acquisition of lists that are novel to those that come from previously learned TI lists, we can answer this question. |
Using a basic Matching to Sample (MTS) paradigm, we've trained monkeys to distinguish between various categories, namely, birds, flowers, felines, and people. When the trial begins, a sample picture appears that the monkey has to touch, and after a brief delay a test screen appears with the target picture (that is, a picture that is the same category as - but not identical to - the sample) and 1, 2 or 3 distractors drawn from the other categories. In the next phase of the experiment, we will transition from a MTS paradigm to a Simultaneous Chaining (simchain) paradigm in order to determine whether category information can acquire ordinal properties. That is, can we train the monkeys to associate a particular place within a list based on category alone? To test this, we will present exemplars of all four categories at once and reinforce responses made to the correct picture in the correct position. One monkey may learn to always respond birds-felines-people-flowers, while another may be trained on people-felines-birds-flowers, for example. More than just examining the limits of learning categories, we want to see whether there is meaningful transfer of information from one paradigm to another.
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