|Year : 2010 | Volume
| Issue : 1 | Page : 30-36
Assessment of hemispheric asymmetry: Development and psychometric evaluation of a chimeric face test
Garima Gupta, Rakesh Pandey
Department of Psychology, Banaras Hindu University, Varanasi-221 005, India
|Date of Web Publication||16-Mar-2011|
Department of Psychology, Banaras Hindu University, Varanasi-221 005
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: Anomaly in hemispheric functioning has been linked with various psychiatric conditions. However, most of the procedures used to assess hemispheric asymmetry in clinical population require special training and/or complex procedures and some of the measures suffer from such methodological problems that undermine their utility for clinical use. Further, the available economical procedures such as chimeric face test (CFT) utilize facial expression of emotions posed by western expressers and are therefore less valid measures in Indian context. Aim: Taking these limitations into account, the present study makes an attempt to develop a CFT (using facial affect photographs of Indian expressers) as an alternative and economical procedure for the assessment of hemispheric asymmetry. Materials and Methods: Using the happy and neutral expressions of eight Indian expressers, 32 chimeric faces were developed by combining the half happy and half neutral expressions. These 32 chimeric faces were presented in pairs (arranged in top-bottom fashion) in booklet form to 225 right-handed participants. Using the contemporary item analytic procedure, finally 22 pairs of chimeric faces that showed satisfactory psychometric properties were retained. These 22 pairs of chimeric faces formed the final CFT. The psychometric properties of the various items as well as that of the whole CFT were found satisfactory. Results: All the items were found reliable and valid as indicated by item-total correlation and alpha-if-item deleted. The internal consistency of the CFT was also found to be highly satisfactory (Cronbach's alpha =.80). Further, the participants on the average showed a right hemispheric advantage on the CFT that provide support to its validity. The findings of intermediate analysis of the data of an ongoing project also provide preliminary evidence for the validity of the CFT. Conclusion : The CFT is a reliable and valid measure to assess hemispheric asymmetry in the processing of facial emotions and may prove to be an economical and useful tool in clinical setting.
Keywords: Chimeric face test, hemispheric asymmetry, facial expression of emotion, perceptual asymmetry
|How to cite this article:|
Gupta G, Pandey R. Assessment of hemispheric asymmetry: Development and psychometric evaluation of a chimeric face test. Ind Psychiatry J 2010;19:30-6
It is well documented that the left and the right cerebral hemispheres differ in their capacity to process various types of information.  For instance, it has been found that in right-handed individuals, the left hemisphere (LH) dominates for processing of linguistic information, whereas the right hemisphere (RH) dominates for processing of non-verbal visuo-spatial configuration and emotional information. ,, Such processing capacity difference between the two cerebral hemispheres has been labeled as hemispheric asymmetry or functional hemispheric asymmetry. Further, the deviation from the normal pattern of hemispheric asymmetry (anomalous hemispheric asymmetry) has been linked with various types of psychopathological conditions. , For example, several studies have documented anomaly in hemispheric asymmetry in patients with anxiety disorders  and depression. ,, However, a wide variation in findings related with anomalous hemispheric asymmetry in psychiatric conditions has also been observed. ,, Amongst the various reasons behind the observed inconsistency in findings, the two important factors are the variation in methodology to gauge hemispheric asymmetry and the methodological problems associated with these techniques.
To assess functional hemispheric asymmetry amongst clinical or psychiatric patients, broadly two approaches have been used - electrophysiological/functional brain imaging and experimental-behavioral. In electrophysiological or functional brain imaging approach, the difference in the level of brain activity is recorded either in resting state or while performing certain task and the difference in the activity level of the two hemispheres is considered as an index of asymmetry. Greater alpha and lower level of regional cerebral blood flow (rCBF) observed over a hemisphere indicates hypoactivation of the given hemisphere, whereas lower alpha power and greater rCBF suggest hyperactivation of the given hemisphere. In experimental-behavioral approach, certain types of information are unilaterally projected to either of the two cerebral hemispheres using some experimental procedures and the observed differences in perceptual accuracy and/or processing speed are considered as an index of hemispheric asymmetry. In this approach, the functional hemispheric asymmetry is inferred on the basis of the observed perceptual asymmetry. For instance, if any information presented to the left visual field (LVF) or the left ear (LE) is processed more accurately and faster as compared to the information presented to right visual field (RVF) or right ear (RE), then this LVF/RE advantage is considered as an indicator of the contralateral hemispheric (right hemispheric in the present case) advantage. 
In experimental-behavioral approach there are several techniques used. However, the two most widely used techniques are the "dichotic listening" procedure and "split-field technique". In dichotic listening technique, auditory stimuli (words or tones) are presented simultaneously to both ears. It is assumed that when two stimuli are presented simultaneously to both ears, contralateral pathways override ipsilateral communication.  Because of this phenomenon, the stimuli presented to the right ear are processed by the LH and stimuli presented to left ear processed by the RH. Thus, a right ear advantage is considered as an index of LH advantage and vice versa. In visual split-field technique, the visual stimuli are presented unilaterally either to LVF or RVF in an experimentally predetermined manner for a brief period of time (time less than that required for a saccadic eye movement, i.e., 150 ms). It is assumed that stimuli presented in any visual hemi-field are projected to and processed by the contralateral hemisphere.  Thus, any visual hemi-field advantage in terms of perceptual accuracy or speed is considered as an index of contralateral hemispheric advantage. More specifically, in this paradigm, the LVF advantage is considered as an index of RH advantage, whereas RVF advantage is considered an indicator of LH advantage. 
The variation in the assessment methodologies has yielded inconsistent findings related to hemispheric asymmetry in psychiatric conditions. For example, findings based on the electrophysiological (EEG) measures suggest an underactivation of the LH and/or overactivation of the RH in depression, ,, whereas studies based on the experimental-behavioral approach demonstrated a reduction in the right hemispheric performance (equivalent of RH hypoactivation) in depression. , Similarly, brain imaging (PET) and rCBF studies have documented LH hypoactivation in depression, ,,, whereas using a behavioral measure of hemispheric asymmetry [chimeric face test (CFT)], researchers have reported an enhanced right hemispheric performance in depression. ,
Moreover, the assessment of hemispheric asymmetry in psychiatric population using electrophysiological approach has also been criticized for several reasons. For example, researchers have often noted that the preparation procedures of EEG studies are perceived as emotionally arousing and aversive by the participants,  and thus, the so-called baseline recording condition in such studies may in fact represent recordings of stressful condition. Keeping these limitations in mind, researchers in this field have suggested to use the traditional and well-established behavioral or performance measure of cerebral laterality for demonstrating hemispheric asymmetry in depression or other affective states.  However, the experimental behavioral measures of hemispheric asymmetry such as dichotic listening and split-field technique are also not economical for clinical use. Such techniques require special training and use of computer and computer based softwares. Further, a lot of logistic preparation is also required to use these techniques that limit its use for assessing hemispheric asymmetry in clinical practice.
Taking these limitations into account, the present study makes an attempt to develop an easy to administer and economical measure of functional hemispheric asymmetry that may prove useful for clinical use. The proposed measure is based on the split-field technique but utilizes the free-viewing condition rather than brief computerized presentation of stimuli. Such measures, however, can be used to assess hemispheric asymmetry in processing of non-emotional and emotional visuo-spatial configuration only (e.g., face and facial expressions of emotions). This approach has earlier been used by several researchers to assess hemispheric asymmetry in processing of facial affects. ,, In this technique, a composite face containing two hemi-faces with different expressions of the same expresser (e.g. half happy and half sad/neutral face) or same expression of different expressers are used. Such composite face is called chimeric face. Each chimeric face and its mirror-reversed image are presented in top-bottom arrangement and the respondents are asked to judge which chimeric face is more expressive.
The CFT proposed to be developed in the present study utilizes happy-neutral chimeric faces, in which the chimeric faces are presented in pairs with the only difference that in one chimeric face the happy hemi-face is presented on the left side and in the other it is presented on the right side of the composite face. While presenting each pair of chimeric faces, the subjects are asked to judge which chimeric expression seems to be happier. Since both chimeras are of same expresser and of same emotional intensity, judging a specific chimeric face as more expressive reveals the effect of visual hemi-field. , For instance, selection of left happy-right neutral face as happier than right happy-left neutral reflects left visual field advantage (i.e., an RH advantage). Further, unlike most of the available CFTs that utilize facial expressions of emotions posed by western posers, the present study uses the emotional expressions of Indian posers. This is considered important as cross-cultural differences have been noted in perception of expression of emotions posed by the expressers of same and different cultural groups. For example, "in-group advantage" in the perception of emotion (a condition where participants are usually more correct in recognizing emotions expressed by members of their own culture than in recognizing emotions expressed by members of a different cultural group) has been noted by several researchers. , Overall, the present attempt to develop a CFT using Indian posers will provide an alternative and more economical measure of hemispheric asymmetry that will prove to be a more valid tool (in the Indian context) than the earlier available CFTs that utilize emotional expression of western posers.
Development of CFT
For the development of the CFT, the first requirement was to get photographs of neutral facial expression as well as the facial expression of happiness posed by the same expressers. Toward this end, we selected photographs of facial affect (smiling face) and neutral expression posed by 11 Indian posers (age range 20-30 years) for another study. These expressions were presented for rating of neutrality or happiness to a small group of undergraduate and postgraduate students (N=15). The review of the ratings given by the respondents revealed that the expressions of happiness posed by three expressers were perceived as expression of neutrality or sadness by most of the raters. Thus, the photographs of these three expressers were not included in the development of the CFT. The photographs of happy and neutral expression of eight posers (five males and three females) were finally selected for making the chimeric faces for the proposed test.
Following the methodology in , chimeric faces were created using Adobe Photoshop 7.0. Before developing the chimeric faces, non-emotional facial cues (e.g., hair, ear, etc.) present in each photograph were cropped in order to control their effect on the perception of facial emotional cues. Each photograph was then split into two equal halves from the middle of the face vertically to produce two hemi-faces from each expression. To ensure consistency in splitting the photographs of facial expression, two points were fixed for determining the midline of the photograph of facial expressions.
After splitting photographs of each expression (happy and neutral) into two hemi-faces (left and right hemi-face), the chimeric faces were developed by combining the right happy hemi-face with left neutral hemi-face and left happy hemi-face with right neutral hemi-face of the same poser. In this way, 16 happy-neutral chimeric faces were generated. Mirror-reversed images of each of this chimeric face were also generated (by flipping the images by 180°) in order to produce a facial expression of equal emotional intensity to be paired with the original face. This procedure finally produced 32 chimeric faces with eight expressers. All the chimeric photographs were then converted into gray scale to control the effect of colors on perception of facial affect. The example chimeric faces generated by using the happy and neutral expression of a poser are presented in [Figure 1].
|Figure 1: Example of happy-neutral chimeric faces (a) Happy hemi-face in the left and neutral hemi-face in the right hemi-field; (b) Mirror reversed image of A. Happy hemi-face in right and neutral hemi-face in left hemi-field|
Click here to view
After the construction of chimeric faces, 32 pairs of chimeric faces were created by pairing each original chimeric face with its mirror-reversed image. Each pair of chimeric faces was then printed on the A4 size paper in top-bottom position. The top-bottom position of each chimeric face pair was counterbalanced in such a way that all the chimeric faces appeared with equal frequency on top and bottom positions. Further, due care was taken to counterbalance the hemi-field wise hemi-facial expression of happiness. Half of the pairs had the chimera with the smile to the participants' left and placed on the top and the other half with the smile to the right and the bottom placement. In this CFT, a rightward response was scored when the chimera with the smile to the subject's right was chosen as happier than when the chimera was having smile to the subject's left. The opposite pattern of responding was scored as leftward response.
| Materials and Methods|| |
Psychometric evaluation of the CFT
The psychometric properties of the said CFT were assessed on a sample of 225 individuals. The details of the methodology and findings are presented below.
Two hundred and twenty-five participants (94 males and 131 females) in the age range 19-48 years (mean = 25.36, SD = 6.997) were recruited for the psychometric evaluation of the CFT. Only those participants were included in the present study who had normal and corrected-to-normal vision and were found to be right handers on the handedness inventory  (whose description is given below). The participants who reported any history of psychiatric illness were excluded from the present study.
The following tools were used in the present study.
Handedness Inventory  was used to assess hand preference of the participants. It asks the respondent to rate the frequency of left or right hand use in performing unimanual activities on a 7-point scale ranging from 1 (always left hand) to 7 (always right hand).
Chimeric Face Test: The chimeric face consisting of 32 pairs of happy-neutral chimera (see the previous section for details) was administered to the participants to assess its psychometric adequacy.
The CFT was administered individually. The CFT was presented in a booklet form before each of the participants. Before presenting the CFT, the participants were instructed that they would be presented a booklet consisting of 32 faces and on each page they would find a pair of photographs of facial expression of happiness. Their task was to determine which of the faces in each pair was happier than the other. After reaching a decision, they had to mark their answers in their answer sheet by putting a tick mark against top if the face presented at the top of the page appeared to be happier than the face presented at the bottom of the page. If the face presented at the bottom appeared to be happier than the top, then they had to put a tick mark against bottom. There was no time limit for this test; however, the participants were requested to do as faster as they could.
The response of each participant was scored as leftward and/or rightward response for each pair depending on their choice. If the participants selected a chimeric face with happy hemi-face to their right side, a rightward response was scored and the opposite (happy hemi-face to their left) was scored as leftward response. A numeric score of 1 was given for leftward response and 0 for the rightward response.
| Results|| |
For final selection of paired chimeric faces, the percentage of individuals showing leftward responses (i.e., right hemispheric advantage) on each pair was computed. Further, the conventional item analysis using item-total correlation and alpha-if-item deleted was also done. The obtained results have been presented in [Table 1]. Since CFT involves perception of facial emotions, the proportion of leftward response is expected to be higher on this test (an indicator of right hemispheric asymmetry). Thus, only those items were retained in the final test on which around 60% individuals showed a leftward response and whose psychometric properties (item-total correlation/alpha-if-item deleted) were in acceptable range.
|Table 1: Item characteristics of the CFT along with percentage of individuals showing leftward response on various pairs of chimeric faces|
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Examination of [Table 1] reveals that 10 pairs of chimeric faces (item no. 2, 3, 4, 8, 14, 17, 19, 21, 29, 32) showed either poor psychometric properties (e.g., low item-total correlation and or alpha-if-item deleted greater than overall alpha of .819) or generated fewer than 60% leftward responses. Such psychometrically weaker items were deleted from the final test. On the remaining 22 items, the item analysis was again conducted and the obtained results have been presented in [Table 2].
It is evident from [Table 2] that all the items of the 22-item version of CFT were psychometrically sound inasmuch as the all the items (except item no. 13) showed item-total correlation greater than .20 and none of the alpha-if-item deleted values were less than the overall alpha coefficient of .80. Item no 13 showed relatively lower item-total correlation (r = .133) and its alpha-if-item deleted value also exceeded the overall alpha by .004. However, the correlation of .133 was found to be statistically significant and the overall gain in internal consistency of scale was negligible (.004), and therefore, this item was not deleted from the final scale. The reliability of the final CFT was found to be psychometrically sound (Cronbach's alpha = .80).
To assess the validity of CFT, laterality quotient (LQ) was computed using the following formula.
This formula gives an LQ between -100 and +100. The negative score indicates greater leftward responses (right hemispheric advantage) and positive score shows greater rightward responses (left hemispheric advantage).
The mean laterality for 22-item version of CFT was found to be -25.45, which indicates that on the average, the participants had shown right hemispheric advantage (leftward responses) on the CFT. Observation of a leftward response on CFT involving processing of emotional information attests the validity of the test.
| Discussion|| |
The present study intended to develop a psychometrical sound and free-viewing measure of hemispheric (perceptual) asymmetry that may prove useful in clinical practice. Toward this end, initially 32 pairs of chimeric faces (a composite face developed by merging half happy and half neutral face of same expresser) were developed. In each pair, the chimeric expressions were same except that one expression was the mirror reverse of the other. In such presentation, it is generally assumed that any face perceived as more expressive than the other in a given pair reflects the difference of the side of presentation of the happy hemi-face. The earlier researches demonstrate that in general, a leftward response is evoked on such a task. A number of previous studies have reported greater leftward responses on CFT involving processing of emotional face information. ,,, Consistent with these earlier observations, only 22 chimeric face pairs were considered valid that evoked leftward response by most of the participants (around 60% or above). These 22 pairs of the chimeric faces were finally retained in the final CFT.
The psychometric properties of the 22-item version of the CFT were found to be highly satisfactory. The item analysis of the final CFT revealed that the item pool of this test is homogenous and all the items reliably reflect right hemispheric asymmetry (leftward response bias). The reliability of the final CFT was also found to be highly satisfactory (Cronbach's alpha = .80). Taken together, these observations suggest that the CFT is a highly reliable tool for assessing hemispheric asymmetry in processing of facial expression of emotions.
The preliminary evidences gathered in the present study also support the validity of the CFT. The negative mean LQ (mean = -25.45) observed in the present study reveals that on the average, participants in this test have shown a leftward response bias (right hemispheric asymmetry) which is consistent with the right hemispheric hypothesis of emotion processing. , The present observation that participants on the average showed greater leftward bias on the CFT is also congruent with earlier CFT studies. ,,, Further, the present CFT involves perception of facial expression of emotions for which right hemispheric advantage has been observed in earlier studies. ,, The present observation of right hemispheric advantage (greater leftward responses) on the CFT provides preliminary evidence for its validity.
Overall, the findings reveal that the 22-item version of the CFT is a reliable and valid measure to assess perceptual (hemispheric) asymmetry in processing of facial expression of emotion. Further, the first author is examining the diagnostic utility of the CFT in depression in her Ph.D. research and the findings of the intermediate analysis are quite encouraging and reveal that consistent with the right hemispheric hyperactivation hypothesis of depression, individual scoring high on Beck Depression Inventory showed greater leftward bias in the present CFT as compared to symptom free controls. This observation provides further evidence for the validity of the CFT. Though the findings of the present study are encouraging, the validity of this measure should be evaluated against other techniques of assessing hemispheric asymmetry such as electrophysiological measures (e.g., EEG) and split-field and dichotic listening techniques in future research. Further, there is also a need to evaluate its diagnostic utility in various clinical populations.
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[Table 1], [Table 2]