Wednesday, April 27, 2011

Essay on Facial Expressions

Essay on Facial Expressions

The aims of this research study are to determine whether an emotional facial expression is more rapidly located in an array of neutral faces, than the location of a neutral face amongst emotional faces. It endeavors to discover which kind of facial expression in particular is most readily located in an array of neutral faces, as well as determining the influence of the overall number of distractor faces present on the efficiency of target face location.


Human facial expressions across cultures appear not to vary, and the facial muscle movements that signify happiness in one area of the world seem to be the same on the other side of the globe, regardless of levels of isolation (Ekman & Friesen, 1971). Darwin proposed that our facial expressions are an unlearned, innate response that has developed from similar expressions in other animals.

Recent studies of the human limbic system have revealed that particular individual emotions like fear and disgust, are processed by certain neural substrates (Calder, Lawrence & Young, 2001). A small almond-shaped structure buried deep in our temporal lobe has a significant role in emotional processing and deficits to it have resulted in an impaired recognition of facial expression (Grossman, E., 2000). It is intriguing that through MRI scans an increase in the amygdala's activity is evident when participants view fearful facial expressions, more so than expressions of happiness, disgust, anger or neutrality (Kassin,K., Heider & Simmel, 1982). Conversely, patient-based studies show that when participants view facial expressions of disgust in particular, brain imaging identifies the insula and basal ganglia to be extremely active during processing (Uller, C. & Nichols, S.).

It has been suggested that emotional facial expressions do not have to be attended to for them to be perceived; it is an involuntary process (Hansen & Hansen,1994., Stenberg, Wilking & Dahl, 1998). In fact Pratto & John (1991) argue that negative expressions attract attention more so than positive or neutral expressions due to an adaptive, automatic recognition of danger that is part of the human biology. One study indicated that angry faces amidst a happy crowd were found more rapidly than a happy face amongst angry distractors (Hansen & Hansen, 1988).

Previous research has also concluded that as the number of distractor faces increase, little or no change is seen in the time it takes participants to locate the target face. This is only true when all the distracter faces have a constant expression.

If facial emotion can be perceived without conscious perception, as suggested by previous studies, then a target face with a unique emotion should summon attention to its location, and should therefore be relatively easy to find amongst neutral distractor faces.

Adding more distractor faces should not substantially increase the difficulty of searching for an emotional face amongst neutral faces, because emotional faces capture attention automatically.

Conversely it should be more difficult to find a neutral face amongst emotional distractors, because the distractor faces are more likely to capture attention than the neutral target.

Participants: All students who are undertaking Laboratory classes for Psychology 512120 at the University of Melbourne.

Face stimuli were taken from Ekman & Friesen (1971) set and presented on a computer display. Half the visual search displays had 3 faces and the rest consisted of 6 faces arranged around a central point in a circle. 50% of the trials contained the target face and the specified target was absent in the other 50% of trials.

Neutral stimuli and four emotional stimuli were present in the search tasks: happiness, sadness, anger and fear.

Participants underwent 160 trials in each of the two experiments.

Before participants underwent the experimental trials, practice trials were given to provide feedback and familiarize them with the procedure. Each participant performed two experiments involving one emotion only. 25% of the group were allocated one of the four emotions; happiness, sadness, anger or fear. Experiment 1 involved searching for an emotional face amongst neutral distractors, while Experiment 2 involved searching for a neutral face amongst emotional distractors. The particular order that each 25% of the group undertook Experiment 1 and Experiment 2 was randomized.

When the target was present, participants responded using the left mouse button, or the right button when they perceived the target as absent. They were instructed to respond as rapidly and accurately as possible; feedback was provided after each response. The computer measured the speed and accuracy of each participant.

Before the correct reaction times were analyzed, participants who made 30% errors, who had response times 200 ms or who had results & standard deviations above the condition mean were excluded.

The Figures that follow firstly show the mean search times for emotional and neutral target faces, note that Display Set 1 involves 3 faces while Display Set 2 involves 6 faces. The Figures also graph the standard deviation for each response; both neutral and emotional in each Display Set situation.

The results indicate that while searching for all four emotions studied, the reaction time for participants to locate an emotional target face is more rapid than the location of a neutral target. Reaction times were quickest for the group who were instructed to locate a happy face in the crowd of neutral faces; 839 milliseconds (3 faces) and 912 milliseconds (6 faces). The slowest reaction times were recorded from participants searching for sad facial expressions; 1268 milliseconds (3 faces) and 1616 milliseconds (6 faces). Overall reaction times grew as the number of distractor faces increased in the case of each separate emotion.

The results indicate participants found it easier to locate emotional faces amongst neutral faces, than a neutral face amongst emotional ones, supporting the hypothesis. It appears happy faces drew attention most rapidly out of all the emotions. These results are inconsistent with Hansen & Hansen's previous research (1989). Unexpectedly, the size of each display seemed to influence the reaction time of participants; slowing down as the overall number of faces grew, which rejects the original hypothesis.

Although the results provide insight into the nature of human emotional processing, interpretation is difficult. There is no clear evidence available to confirm that the speed in which we automatically attend to and locate emotional faces is due to the actual emotion. It has been suggested that humans are drawn to faces expressing emotion because of distinct facial features or components (Byrne & Eysenck, 1995; Nothdurft, 1993; Purcell, Stewart & Skov, 1996; White, 1995).

A trend is present in the results supporting one hypothesis and indeed rejecting one, but only to a certain extent. The difference between reaction times cannot be considered significant. It must also be considered that the participants were a convenient sample of Melbourne University students, learning about psychological research methods and were well-informed on previous research and the predictions for this experiment. A self-fulfilling prophecy may have occurred and students possibly unconsciously slowed their reaction times when locating neutral targets. Each group of participants were instructed by 4 different experimenters (tutors). The conditions may not have been constant in each group therefore the results for each individual emotion may be affected.

It is important to note that in light of the results no clear conclusions or inferences can be made due to their statistical significance. Interestingly faces displaying happiness were attended to faster than those displaying sadness, anger and surprisingly fear. Changing the overall number of distracters did appear to change the speed of reaction time, which was not originally expected. However, the trend in the data gathered is also indicative that emotions are rapidly attended to; they play a functional role in guiding our focal attention, perhaps an important adaptive human element.

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