The Reverse Stroop Effect

Attention according to Daniel Gopher is “the scientific term primarily used to describe all processes and mechanisms that govern the subjective constraints imposed by the human organism on the flow and interpretation of external and internal information, and on the organization and selection of responses, in the service of goal-directed behavior. In some cases, attention can also be automatically captured by sudden changes in the situation, or by well-trained stimulus–response tendencies.”

Attention can also be defined as the ability to selectively process sensory information actively from the enormous amount of information available through our senses, our stored memories, and our other cognitive processes (De. Weerd, 2003(Best, 1999)The
neural basis of attention lies in the capacity of the brain structures that represent the behavioral relevance of stimuli to alter sensory processing. This refers to its ability to effectively process relevant information whilst ignoring irrelevant stimuli. One of the earliest research studies done on attention was that in 1894 by Hermann von Helmholtz. Though, several attempts have been made to define attention, it must be noted that attention is not a unitary cognitive ability. There are different kinds of attentions, and depending on the cognitive tasks, the brain activates different neural networks. (De Weerd, 2003).

Cognitive psychologists studying attention are concerned primarily with cognitive resources and their limitations. According to research conducted on attention, it was found that, people have only a certain amount of mental energy to devote to all the possible tasks and all the incoming information confronting them. If thus if an individual devotes some portion of those resources to one task, less is available for others. The more complex and unfamiliar the task, the more mental resources must be allocated to that task to perform it successfully. (Galotti, n.d.)

The earliest work on attention and interference can be seen in James Cattell’s (1886) study, wherein, subjects were meant to say out loud the name of the color (eg “red”) for a patch of color as well as read out loud the name of the color (eg. “red” written as “red”) Results showed that reading the word red out loud was significantly faster than naming the patch of color. Though the research isn’t directly linked to Stroop’s experiment, there is similarities found in the underlying basis of the task i.e., color naming. Another aspect, which has been seen by researchers as a profound and far ahead of its time, is Cattell’s explanation of the phenomenon. He address the concept of automaticity of cognitive processes i.e., he attributes the significantly lower reaction time to practice which then makes the reading of the word seem effortless and unconscious. Research following the study (eg. Lund 1927, Brown 1915, Hollingworth1912, Ligon 1932.) attempted to provide alternative theories.

One of the classic and pioneering experiments to in the study of selective attention, interference and automaticity ie the way we perform some mental tasks quickly and effortlessly, with little thought or conscious intention. (Palmeri, 2003) is what is now known as the phenomenon of the Stroop Effect. In 1935, John Ridley Stroop article ‘Studies of interference in serial verbal reaction’ first put forth his hypothesis on “A comparison of the interfering effect of color stimuli upon reading names of colors (the two types of stimuli being presented simultaneously) with the interfering effect of word stimuli upon naming colors themselves…. The increase in the time for reacting to words caused by the presence of conflicting color stimuli is taken as the measure of the interference of color stimuli upon reading words. The increase in the time for reacting to colors caused by the presence of conflicting word stimuli is taken as a measure of the interference of word stimuli upon naming colors.” (Stroop, 1935). His second hypothesis, which incidentally stemmed from the first and also prior research was based on the question that “What effect would practice in reacting to the color stimuli in the presence of conflicting word stimuli have upon the reaction times in the two situations described in the first problem.” (Stroop, 1935). The key difference between Stroop’s experiment and that of his predecessors was that his participants were presented with “pairs of conflicting stimuli, wherein both were inherent aspects of the same symbols, these were presented simultaneously (a name of one color printed in the ink of another color -- a word stimulus and a color stimulus). These stimuli are varied in such a manner as to maintain the potency of their interference effect.” (Stroop, 1935)

In the experiments conducted, the most important feature and that which has been replicated in various studies of psychology, along with the study that follows, is the material and method of Stroop’s original work. He used what he called "Reading color names where the color of the print and the word are different" (RCNd), and "Reading color names printed in black" (RCNb) tests to measure the effect of interference. In his first experiment, he used the colors red, blue, green, brown, and purple after consultation with Dr. Peterson. In his study he further details characteristics of the test. “the colors were arranged so as to avoid any regularity of occurrence and so that each color would appear twice in each column and in each row, and that no color would immediately succeed itself in either column or row.” This was even followed in the current experiment where a randomized order was selected so as to avoid a pattern and to keep the participants alert. In his original study, “The words were arranged in such a manner that the name of each color would appear twice in each line. No word was printed in the color it named but an equal number of times in each of the other four colors; i.e. the word 'red' was printed in blue, green, brown, and purple inks; the word 'blue' was printed in red, green, brown, and purple inks; the word 'blue' was printed in red, green, brown, and purple inks; etc. No word immediately succeeded itself in either column or row. The test was printed from fourteen point Franklin lower case type. The word arrangement was duplicated in black print from same type. Each test was also printed in the reverse order, which provided a second form.”(Stroop, 1935)

Results showed that there was only a difference of 2.3 seconds or 5.6 percent as the increase in time taken to read the color word as against the same word printed in black. The difference in time was two small to be reliable. A recent replication of the study was conducted by MacLeod where in no interference was found in naming of incongruent color words. (C.M. MacLeod, 1991)

In Stroop’s second experiment where, the “Naming color Test” and the "Naming color or word test where the color of the print and the word are different" (NCWd). Test was employed. During the experiment, subjects were tested only on naming colors of incompatible words and of control patches. Here, the hypothesis i.e., the interference is expressed by measuring the difference between the times of the NC and NCWd cards. Total time per card would then be divided by number of stimuli on the card. This is occasionally used to estimate time taken per stimulus.(C.M. MacLeod, 1991) Results showed mean time of the responses increased from 63.3 seconds to 110.3 seconds or an increase of 74 percent. The standard deviation is increased in approximately the same ratio from 10.8 to 18.8. The coefficient of variability remains the same to the third decimal place (s / m = .171).(Stroop, 1935). It was found that that 99 percent of the timings on the experimental cards exceeded that of the control cards.(C.M. MacLeod, 1991)

In his third experiment, which according to MacLeod was considered his most complex experiment, addressed his second hypothesis of “Practice Effect” on the color-naming task. (C.M. MacLeod, 1991) The study, was conducted over a period of 8 days in order to see what effect would the repetition and thus practice have on the reaction time of the subjects. It was found by Stroop (1935) that over the days the times decreased by16.8 s from 49.6 s to 32.8 s. Thus, interference from incompatible words appeared to decrease with practice. However as MacLeod points out there could be a general practice or learning- to-learn effect here: Ink color-naming baselines were not collected each day.

Stroop also explored the “impact of practicing color naming on the development of interference in word reading.” (C M MacLeod, 1991).
This aspect of his study that later came to be called the “Reverse Stroop Effect” as it was seen in a comparison between pre and post tests that the subjects who had been reading the incongruent color words for the 8 days of the experiment, now faced an interference in word reading (from 19.4 s before to 34.8s after) however this interference disappeared after the second post test. (22.0 s) (C.M. MacLeod, 1991; Stroop, 1935). This can be attributed to the automaticity theory, which states that reading due to practice is an automatic response and thus doesn’t require attention, however due to the practice the words for a short period became the automatic response, the reverting, can be attributed to the years of practice the subjects have of reading as compared to the week they had for the task. Stroop (1935), attributes this difficulty or the interference to adult, literate participants have had so much practice reading that the task requires little attention and is performed
rapidly.

With regard to The Stroop Color – Word Interference Test, research following Stroop’s original work has seen many variations and modifications. There have been debates with regard to the scoring, reliability and variability of the study.(C.M. MacLeod, 1991) On the debate of scoring of the Stroop effect, many complicated (e.g., Smith, 1959; Smith & Borg, 1964; Smith & Klein, 1953) as well as basic techniques were evaluated. However, studies, especially that by Jensen and Rohwer (1966)have found that the key approach is to calculate a difference score (interference card time - pure color card time) following Stroop (1935b).

Debates with regard to the reliability and variability have been highlighted in Macleod’s article.
Sjoberg (1969,1974) using regression analyses of various clinical populations has found support for the reliability and validity of the Stroop Color-Word Test. Other researchers (eg. Smith, Nyman (1974); Sehubo, Hentschel (1977, 1978); Uechi (1972); Santos, Montgomery (1962) directly assessed the reliability of the test Results showed that it was uninfluenced by events interpolated between test and retest. (C.M. MacLeod, 1991). Although it has been considered by Jensen (1965) as one of the most reliable psychometric tests, there have been studies, which find fault in it. Research by Zajano, Hoyceanyls, and Ouellette (1981 ) has shown that ink color and shape change repeatedly on the standard interference card, however only ink color changes on the standard control card. Changing shapes on the control card to correct this confound did not alter the basic effect, however. Sichel and Chandler (1969) argued that alternatives over stimuli was too great in the standard test; their procedure using pairs of stimuli and firmer controls on hue, brightness, and so forth also left the basic pattern intact.(C.M. MacLeod,
1991).

In his original study, Stroop interpreted his data as follows :

“The associations that have been formed between the word stimuli and the reading response are evidently more effective than those that have been formed between the color stimuli and the naming response. Since these associations are products of training, and since the difference in their strength corresponds roughly to the difference in training in reading words and naming colors, it seems reasonable to conclude that the difference in speed in reading names of colors and in naming colors may be satisfactorily accounted for by the difference in training in the two activities. (Stroop, 1935b, pp. 659-660).”

Thus concluding from his third experiment, Stroop attributes his results to a practice effect created due to training in reading words rather than color naming. Stroop used his experiments to explain the asymmetry of interference. As in the incongruent condition, words interfere with color naming but colors do not interfere with word reading i.e., words do evoke a single reading response as explained by Peterson etal (1925) whereas colors evoke multiple response, which in turn makes naming colors slower than reading words. (C.M. MacLeod, 1991). According to Stroop, literate adults read so quickly and effortlessly that not reading words is hard. Thus when confronted with items consisting of words, participants couldn’t help reading them