The habituation technique is one of the core methods used in psychological research to study the cognitive development of infants. On the one hand, this modus operandi helps us to determine the existence of a specific cognitive and perceptive process in infants. On the other hand, an erroneous or inaccurate interpretation of the process will certainly result in wrong conclusions which could mislead the direction of future studies. Hence, this technique should be used scrupulously, due to the fact that alternative designs and/or procedures of the same study can lead to different results.
The aim of this essay is to highlight the importance of examining all the variables that influence the outcomes of a study. To begin with, this essay will illustrate and analyse the habituation technique in general terms; secondly, it will focus on one case study by Schwartz & Day (1979) which uses this method. Finally, in order to reveal some of the weaknesses of the above study, this essay will offer an alternative explanation for the results developed by Cohen & Younger (1984), followed by a further consideration.
Due to the fact that infants cannot communicate their feelings as adults do, a method is needed to apprehend what and how infants are able to perceive from the physical and social world (Bremner, 2003). The habituation technique measures behaviour through direct observation, a procedure used by researchers to obtain data by watching carefully and reporting the information acquired, explained by Glassman & Hadad (2004) as a strategy to gather information in a way that does not take into consideration what the individual says.
Thus, it can be considered as a valid procedure for experimental research in infants. The habituation phenomenon is related to the gradual decrease in response recovery of an individual over a frequently repeated exposure to a stimulus (Messer, 2008). To exemplify, if a visual stimulus is repeatedly showed to an infant, it will be seen that its attention will steadily decrease: this phenomenon is called habituation and in this case can be related to the existence of a visual memory (Bremner, 2003).
To prove this theory, a new stimulus should be presented to the infant, and if the looking time increases (dishabituation) it is true to say that it can discern between two objects, and thus that it possesses a visual memory (Bremner, 2003). This method can be used to evaluate the infant faculties of sight, smell and hearing by changing the features of the habituated and novel stimuli (Benbersky & Sullivan, 2007).
One of the most controversial problem of the habituation technique concerns the case in which the tested infant shows an increase in responsiveness rather then a decrease in the response recovery of a frequently repeated stimulus, a process called sensitization (Groves & Thomson, 1970). A solution to this issue can be deducted from the studies of Groves & Thomson (1970) on habituation (Schwartz & Day, 1979), where they postulate habituation as a dual process theory, in which there is a co-existence of two divergent procedures, namely habituation and sensitization (Groves & Thomson, 1970).
The two researchers founded their hypothesis on behavioural and physical evidence asserting that both habituation and sensitization (behavioural evidence) are linked to the somatic part of an individual through interneurons (physical evidence) defined as plastic since they are adaptable to change (Schwartz & Day, 1979). Groves & Thomson (1970) argue that the most influential factors in shaping the above processes are the intensity and the frequency of a stimulus, with sensitization prevailing when the former is high and habituation prevailing when the latter is high.
Therefore, in order to obtain habituation, the different sets of stimuli presented in a test will need to have an even or similar level of intensity and frequency (Schwartz & Day, 1979). To have a practical idea of habituation, the study conducted by Schwartz & Day (1979) will now be analysed. The habituation pattern was utilized by Schwartz & Day (1979), with a study involving nine experiments, to investigate visual shape perception in infants aged between 2 and 4 months old.
This paper will focus on their first experiment, which concerns in finding out which aspects infants look at in order to recognise a shape (a two-dimensional figure). The two researchers want to understand whether infants are able to discriminate the angular relation of two edges. Moreover, they argue that infants perceive shapes as a whole by adding a further prediction “based on the assumption of the equality and additivity of stimulus dimensions” (Schwartz & Day, 1979, p. 14). Infants condition is very important and for this reason the experiment can only be conducted when it maintains calm and attention Schwartz & Day, 1979). The four stimuli given in the experiment were: A composed of two segments forming a 90° angle (habituation stimulus); B and C both having a characteristic in common with A, but with the former differing in the orientation of the edges and the latter differing in the angle (it is generally oriented as A); D is varying in both angle and orientation of the contours in respect to stimulus A, and it also has the peculiarity of having its angle size in between A and C (Schwartz & Day, 1979).
The problem of sensitization was solved by introducing an separate additional control group to test the four stimuli, with the results showing equal sensitization and habituation properties (Schwartz & Day, 1979). The visual fixation time was measured and used as data to establish whether habituation had occurred and if the hypothesis were true. In order to reduce any misleading influences in the results, possibly caused by confounding variables (e. g. in infants: fatigue, boredom, etc. (Howitt & Cramer, 2008), Schwartz & Day counterbalanced the stimuli by changing the sequence of test stimuli: four presentation orders were showed to four different sex-balanced groups. Each stimulus was showed for 20 seconds, with a red plain slide interval of 5 seconds between one another. However, stimulus A was indicated as the habituation figure, and thus, it was showed to infants 8 times, subsequently, and without any ulterior interval, the four test stimuli (A, B, C, and D) were presented one time each (Schwartz & Day, 1979).
After that habituation was verified, the researchers predicted that infants would discriminate stimulus C, and that stimulus D would be the one with greatest response recovery. The final outcome showed that: A had the lowest response recovery (9. 69 sec); C had the greatest response (14. 99 sec); B and D presented similar responses (12. 58 sec and 13. 03 sec). The results were not totally in agreement with Schwartz and Day predictions, in fact, infants discriminated C with an outstanding response recovery rather than D.
The researchers interpreted this data by saying that the angular relation and not the orientation of two edges is the main discriminatory variable to be considered in infants shape perception (Schwartz & Day, 1979). In the experiment by Schwartz & Day there is a conflict between predictions and results, which constrained them to reconsider their hypothesis and to give a new explanation of the phenomenon. However this cannot be considered enough, since a critical analysis of the study is needed to clarify and/or verify the matter in question.
Cohen & Younger (1984) underlined a possible wrong aspect of Schwartz & Day’s work and tried to offer an alternative explanation based on the evidence of their own experiment. They argued that the set stimuli used by Schwartz & Day were ambiguous about the angular relation of the two segments and the orientation of the single segment in respect to habituation stimulus: the angle of B has each of the two segments in the same orientation as A, the stimulus is just rotated of 90° in respect to A; C does not present any segment in the same orientation; D presents one segment in the same orientation as A (Cohen & Younger, 1984).
Therefore, the aim of Cohen & Younger was to elucidate Schwartz & Day’s work through the presentation of a new set of stimuli tested on 3 months old infants, which now possess a better design of the representative figure. The procedure and apparatus remained the same as the previous experiment, as well as the characteristics of the new stimuli, with the only change being in the segments now placed in different positions.
The experiment results completely match with Schwartz & Day previous predictions, in fact stimulus D (differing in angle and orientation of the edges from the habituation stimulus) had the greatest response recovery and stimulus C (differing in the angle relationship of the edges from the habituation stimulus) had also an high mean in response. It also showed that stimuli A (habituation stimulus) and B (differing in edges orientation) had the lowest response and besides a similar mean, therefore, infant did not respond to the orientation of two edges.
Cohen & Younger concluded that, with a repetition of Schwartz & Day’s experiment by using a more suitable composition of the stimuli segments, the new results supported Schwartz & Day position better and more precisely than the outcomes of their own first experiment. It follows a further consideration: in Cohen & Younger (1979) study two infants, after a verified habituation, looked longer at the habituation stimulus during the test phase, creating an anomaly.
Therefore, is it correct to interpret this data as a mean number as researchers do or should it be considered as a moot point in critically detecting weaknesses in the study, since shape perception is seen as extremely personal? To conclude, even though habituation is a valid method to investigate infants perception and cognitive abilities, a detailed verification of all the variables of the entire process is essential to achieve reliable results, together with a critical analysis of the study which can open to further considerations and new approaches.