Simply Amazing!

In the natural setting, we are bombarded by a large amount of sensory input, which makes great demands on the processing ability of the human brain. Have you ever wondered how our speech perception system deals with this complexity. The following research by Laukka(2005) demonstrated categorical perception in which given a wide range of stimuli, human beings are able to classify them into limited number of categories.

Anger, fear, happiness, and sadness were the emotions used in the study. Discrimination and identification tests were performed. In the discrimination tests, participants were asked to discriminate between pairs of expressions in this form, ABX, by deciding whether X is the same as A or B. In the identification test, the listeners were asked to judge the emotion of each synthesized expression by means of forced choice. The alternatives that the listeners could choose from were the same as the two end-emotions of the continuum to which the respective expression belonged.

The results for the identification part revealed that every continuum fell into two clear regions. Each region corresponded to the emotion category of the prototype, with an abrupt shift from one category to the other around or at the center of the continuum.

In the discrimination tests, peak pairs were easier to discriminate than non-peak pairs. In addition to this, for all continua, discrimination for peak pairs were more accurate as compared to non-peak pairs.

To put things together, the results showed that identification and discrimination are not independent. Meaning, the identification performance, to some extent, predicted the discrimination performance.

Due to the limitation of the procedure in the first experiment, highly demanding to the short-term memory that could probably affect the results, the researchers made a slight modification of the procedures in experiment one so as to eliminate the said problem. For this part, the decoding accuracies for all synthesized expressions were gotten. The results were consistent as with the results of the first experiment for the identification test. The discrimination test also provided similar results as with the results of the first experiment such that peak pairs were favored.

All in all, Identification results revealed that the continua were perceived as 2 distinct sections separated by a sudden category boundary. Also, discrimination accuracy was generally higher for pairs of stimuli falling across category boundaries than for pairs belonging to the same category. These results suggest that vocal expressions are perceived categorically.

In reality, I had difficulty comprehending the research since it is highly technical, and I believe that my background on perception is not sufficient to understand easily the ideas and concepts presented in this study.


Source:
Laukka, P., (2005). Categorical Perception of Vocal Emotion Expressions. Emotion, Vol. 5, 277-295.