discrimination-shift problems background this type of task has been used to compare concept learning...

Discrimination-Shift Problems

Background

This type of task has been used to compare concept learning across species as well as across a broad range of ages among humans, from pre-school age to adulthood. The findings give us insights into the nature of intellectual growth. The basic question is whether the subject learns a discrimination by rote or by forming a concept based on the common attributes of the positive instances (discriminative stimuli in behavioral terms).


Background

It’s a 2-Phase procedure:

Phase 1: On each trial the subject is presented with two stimuli that differ along two or more dimensions, such as shape, color, and size. Choice of one of those stimuli is reinforced; choice of the other is not. Trials continue until the subject consistently makes correct responses, i.e., shows a discrimination.


Background

It’s a 2-Phase procedure:

Phase 2: The problem is changed, either by presenting a new set of stimuli or by presenting the original stimuli but changing the correct choices. Based on the rate at which the second discrimination problem is learned, an inference is made as to how the subject solved the first problem, either by rote or by forming a concept.


Phase 1

For all of the problems to be discussed, Phase 1 will consist of the following stimuli:

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Half the trials present a red square and a green circle. Choice of the red square is reinforced.The other trials present a green square and a red circle. Choice of the green square is reinforced.


Phase 1

The positions of the stimuli on the left and right sides are changed randomly across trials. +

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How would you describe the correct choice in this problem?If you said, “the “square”, then you looked at the problem conceptually. “Square” is the attribute shared by the positive instances of the concept.


Phase 1

By saying “square”, you were ignoring the irrelevant attributes of red and green.

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Will subjects similarly ignore the irrelevant attributes and respond only to the relevant one?In theoretical terms, what processes give subjects this ability to separate relevant from irrelevant attributes?


Phase 1

In theoretical discussions, researchers use the terms “relevant dimension” and “irrelevant dimension”. A dimension is like a variable that is divided into levels or conditions.

Color is a dimension. The red and green attributes are subdivisions of the color dimension. Shape is another dimension. Square and circle are subdivisions of the shape dimension.


Phase 1

A dimension is relevant if choosing an attribute of that dimension is always correct:

Shape Dimension

Square

Circle

SquareAlways Correct

Circle Never Correct

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Phase 1

A dimension is irrelevant if choosing an attribute of it is correct only half the time:

Color Dimension

Red Green

Red Correct Half the Time

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Green CorrectHalf the Time


Phase 2

After subjects learn the first discrimination problem, a second problem is presented. It often involves presenting completely different stimuli than were used in the first problem. However, the two problems are conceptually related. There are two versions of the second problem. The stimuli are the same but the solutions are different. One is called an intradimensional shift (IDS) and the other is called an extradimensional shift (EDS). Half the subjects get the IDS and half get the EDS.


Phase 2

On an intradimensional shift, the dimension that was relevant to the solution in the first problem remains relevant in the second problem. In the present example, this is the shape dimension.On an extradimensional shift, the dimension that originally was relevant becomes irrelevant. The correct choice is on the other dimension (color). Here are examples of an IDS and an EDS.


Phase 2

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IDS EDS

For the IDS, the correct choice is “triangle”.

For the EDS, the correct choice is “blue”.


Phase 2

Generally, it is found that nonhuman species and humans of different ages learn the IDS faster than the EDS.

Considering that the stimuli in Problem 2 are completely different from those in Problem 1, why should one shift be easier than the other? It is because subjects saw shape as the relevant dimension in Problem 1 and then continued to focus on the shapes of the stimuli in Problem 2. This was an advantage for the IDS but a disadvantage for the EDS.


Phase 2

In the presentation on Transfer we saw how Harlow’s monkeys acquired a “learning set” as a result of solving a lot of two-choice discrimination problems. They learned to approach each new problem in way that gave them the solution in the fewest possible trials.

Research with the IDS and EDS similarly shows the formation of a learning set. For the IDS it facilitates learning but for the EDS it interferes.


Phase 2

In some discrimination-shift problems, the same stimuli that were used in Phase 1 are used in Phase 2. Solutions are changed in ways similar to the IDS and EDS but the pattern of results across species and ages is completely different.


Phase 2

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In a reversal shift (RS), the dimension that was relevant in Problem 1 continues to be relevant in Problem 2 but the correct choice is the opposite attribute on that dimension. In the present example, shape would be relevant and the correct choice would be shifted from square to circle.

Original Problem


Phase 2

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In a reversal shift (RS), the dimension that was relevant in Problem 1 continues to be relevant in Problem 2 but the correct choice is the opposite attribute on that dimension. In the present example, shape would be relevant and the correct choice would be shifted from square to circle.

Reversal Shift


Phase 2

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In a nonreversal shift (NRS), the previously irrelevant dimension (color) becomes relevant and the subject must learn to choose the correct attribute on that dimension. In the present example, it’s green.

Original Problem


Phase 2

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In a nonreversal shift (NRS), the previously irrelevant dimension (color) becomes relevant and the subject must learn to choose the correct attribute on that dimension. In the present example, it’s green.

Nonreversal Shift

Note that only 2 of the 4 responses have to be changed.


Phase 2

Quick Quiz

In each blank, fill in IDS or EDS:

A reversal shift is a type of _________ and a nonreversal shift is a type of ________.

The reason is:

In both the RS and IDS the same dimension is relevant to the solution in Problems 1 and 2. In the NRS and EDS, the dimension that was relevant in Problem 1 is irrelevant in Problem 2.

IDS

EDS


Phase 2

Which do you think is easier, the RS or the NRS? In the RS you have to change all 4 responses but in the NRS you have to change only 2. IT DEPENDS ON WHO THE LEARNER

IS ...NRS Learned Faster than RS NRS = RS

RS Learned Faster than NRS

Nonhuman species

Preschool children

Kindergarten children

1st Graders

Older children

Adults


Interpreting RS vs. NRS

NRS Learned Faster Than RS

This indicates that the subjects did not form a concept in the first problem. Instead, they memorized the complete stimulus and the response that went with it, for example, approach red square and avoid green circle.

In the RS, the subjects have to change 4 of their responses in Phase 2 whereas in the NRS they only have to change 2 responses.

The subjects’ choices are controlled by both the relevant and irrelevant attributes of the stimulus.



RS Learned Faster Than NRS

This indicates that the subjects formed a concept in Phase 1 by separating the relevant dimension (shape) from the irrelevant dimension (color). In the RS, they started out focusing on the relevant dimension and just had to switch to the opposite attribute on that dimension (circle). In the NRS, they started out focusing on the irrelevant dimension. They had to switch to color and then learn to choose the correct attribute on the color dimension (green).



In research with the IDS versus EDS, rats and very young children perform like adults: They learn the IDS faster. Why don’t they learn an RS faster than an NRS and show similar evidence of concept learning?

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Rats and young children separate shape from color to some extent but they do not block out the irrelevant attributes, red and green, as much as adults do.

Original Problem


When the identical stimuli appear in Problem 2, these irrelevant attributes continue to influence their choices.


Why do adults and rats show different patterns of results on these problems? The processes responsible for adult performance appear to develop gradually during childhood: Preschoolers perform like rats, but by the age of about 7 years, children perform more like adults.

The Role of Language

According to one influential theory (Kendler & Kendler, 1962), the underlying processes involve the ability to use language. Solving the problem conceptually is said to involve two steps:


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1. The subject labels the relevant attribute or dimension.


Its the square.

2. That label then controls the subject’s choice response. It “mediates” between the external stimuli and the observed behavior.

The label alone is not enough. Young children are sometimes found to verbalize the correct attribute but then make the wrong choice. There is a disconnect between their speech and their behavior.


That 4-year-old children can be trained to use verbal mediating responses was shown in an experiment by Kendler and Kendler (1962).


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There were just two stimuli in Phase 1. The large-black square was correct and the small-white square was incorrect.


Group L was instructed to say “Large” when they chose the positive stimulus. Group B was told to say “Black”. Of course, at this point, both labels were correct. Group NV was not instructed to verbalize an attribute.


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In Phase 2, there were two types of trials. The small square was always correct.


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Theoretically, Group L came into Phase 2 verbalizing the right dimension and just had to reverse attributes. Group B had to switch to the size dimension and then figure out the correct attribute. Group B should take more trials to learn Problem 2.


Results


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Group L learned fastest. Group B showed the slowest learning, taking twice as many trials as Group L. Group NV was in the middle.


Interpretation


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Group L performed like adults learning a reversal shift. Group B performed like adults learning a nonreversal shift. Group NV differed from the others because their choices were not mediated by speech.


Perceptual Learning

Perceptual learning is an increase in sensitivity to the features that distinguish one stimulus from another as a result of prior exposure to those stimuli.

There is evidence that giving children perceptual training with the stimuli that will be used in a discrimination-shift problem can make their performance more like an adult’s and less like a rat’s.


Perceptual Learning

In an experiment by Tighe (1965) with 1st graders, the stimuli were glasses that differed in height and brightness. Before starting Problem 1, half the children were given perceptual training to help them distinguish height from brightness.They were shown one glass. Then it was removed and another presented.


Perceptual Learning

The child was asked if the two glasses were the same or different. There were not told if they were right or wrong.

In one series of comparisons, the glasses differed only in height.


Perceptual Learning


In another series, they differed only in brightness.


Perceptual Learning


In the final series, the glasses differed on both dimensions.


Perceptual Learning

Theoretically, this should help the child separate “small” from “light” and “dark” in the example below.

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Children who did not receive perceptual training learned reversal and nonreversal shifts at equal rates. Children who received the perceptual training learned the RS 3 times faster than the NRS, like an adult.

Results


Perceptual Learning

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Perceptual training is often included in preschool programs. It’s emphasized in Montessori schools. Tighe’s experiment shows that it is beneficial: It promotes concept learning.Perceptual training and training in naming attributes both can make important contributions to early childhood education.

discrimination-shift problems background this type of task has been used to compare concept learning...

Documents

discrimination problem

irrelevant dimension

green square

red square

correct circle

phase procedure

time slide

terms relevant dimension