Feb 12 2018


SOCIAL PSYCHOLOGY: Racism toward straight lines (Part 1)


In years to come we will probably hear more and more about gender and racial discrimination.

Before trying to tackle these complex issues we need to have a clear knowledge of what constitutes a process of categorization (and consequent labeling) that underlies any discriminatory phenomenon.

The discipline that deals with these and many other issues has the label of “Social Psychology” and bases its theories in a rich heritage of experiments that unravel from the first half of the ‘900 to the present day.

At the same time that social psychology develops, the positivist and behaviorist illusion that sees human beings as perfectly programmed and programmable machines begins to decline.

In fact, humans do not acquire the information by recording it faithfully from the flow of data coming from an external and objective reality, as a video camera would, but they build subjective reality by carefully selecting the information according to the meaning that it represents for each individual.

This process does not only apply for complex phenomena such as interactions between social or ethnic groups but also for basic phenomena such as the visual estimation of a measure.



The 1963 experiment by Tajfel and Wilkes gives us an elementary demonstration of the phenomenon.[1]

The two scientists present a series of 8 lines to a group of English students.

The first line measures 16.2 cm and the following ones measure each 5% more than the previous one, up to the last that measures 22.8 cm. Students obviously do not know this and must estimate their length by eye.

The lines without categorization from the experiment: TAJFEL, H. and WILKES, A. L. (1963), CLASSIFICATION AND QUANTITATIVE JUDGEMENT.


Then they divide the students into 3 experimental groups:

  1. To those of the first group they present the lines as they are without adding anything. This control group serves for comparison with the other two.
  2. To those of the second group they present the lines with a random categorization, i.e. they randomly associate each line to the letter A or to the letter B.
  3. To those of the third group they present the lines with a systematic categorization, i.e. they associate the letter A for the first 4 shortest and the letter B for the other four longer ones.


lines experiment


Scientists hypothesize to find two effects in this experiment: An intracategorial assimilation and an intercategorial accentuation.

In other words, they expect that the students of the third group (to which they present the lines in an orderly categorized manner) will judge as more similar two close lines belonging to the same category, judging instead as less similar the lines 4 and 5 that, despite being as close as the previous ones, belong to two different categories.

The lines 2 and 3 should therefore seem more similar than the lines 4 and 5 even if the difference in length measures objectively the same (5%).

In this experiment only the second effect emerges: even if the students can correctly estimate the lines belonging to the same category (no intracategorial assimilation), they misjudge the lines 4 and 5 (intercategorial accentuation) because they consider them very different due to the fact that they belong to two distinct label categories.

The intercategorial accentuation could emerge from a phenomenon called “assimilation to the central tendency“: the characteristics of the members of a group seem similar to the characteristics present on average in the group itself.
If a group contains short lines, all lines seem similar to the average length, even the longest and the shortest ones that lie at the opposite ends of the group.

Let us pause now to make a small reflection on the experiment. The scientists turned to English students, accustomed to using the imperial measurement system, and asked them to estimate the measurement in centimeters. What would have happened if they asked them to estimate the inch measurement as used in England?


The answer comes from a second experiment on the lines made 40 years later by different social psychologists. This time it includes 3 parameters.[2]



Scientists recruit 2 groups of students: Belgians (accustomed to measuring in centimeters) and Americans (accustomed to measuring in inches).


The experiment involves 2 different categorization scenarios. In the first case the lines appear without categorization, while in the second one they appear in an ordered categorization (A=4 small lines; B=4 large lines).


The measurement takes place in 2 different ways: a group of students must estimate the measurement in centimeters and the other in inches.

So we have 2x2x2 = 8 different situations.


Result scenarios from the experiment: ON THE ROLE OF FAMILIARITY WITH UNITS OF MEASUREMENT IN CATEGORICAL ACCENTUATION: TAJFEL AND WILKES (1963) REVISITED AND REPLICATED. Olivier Corneille, Olivier Klein, Sophie Lambert, Charles M. Judd.

Scientists predict that:

  1. They will influence students’ judgment when the ordered categorization appear (just as in the previous experiment).
  2. They will register a higher effect when students have to make an estimate using a unit of measurement different from the one they usually use.


The results of the experiment confirm this predictions: the ordered categorization has a greater effect when the students have to use a unit of measurement different from their own.

This means that categorization processes and stereotypes in general have more grip on people when they act in a situation of uncertainty in which they have little information.

In the second part of this article we will see how in addition to the categorization itself, also the type of label that we attribute to the categories affects our judgment.



1️⃣ TAJFEL, H. and WILKES, A. L. (1963), CLASSIFICATION AND QUANTITATIVE JUDGEMENT. British Journal of Psychology, 54: 101–114. doi:10.1111/j.2044-8295.1963.tb00865.x [Read it here]
2️⃣ ON THE ROLE OF FAMILIARITY WITH UNITS OF MEASUREMENT IN CATEGORICAL ACCENTUATION: TAJFEL AND WILKES (1963) REVISITED AND REPLICATED. Olivier Corneille, Olivier Klein, Sophie Lambert, Charles M. Judd. Psychological Science. Vol 13, Issue 4, pp. 380 – 383. First Published July 1, 2002 doi:10.1111/1467-9280.00468 [Read it here]


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