Neonatal facial expressions in response to different qualities and intensities of gustatory stimuli

INFANT BEHAVIOR AND DEVELOPMENT 6, 4 7 3 - 4 8 4 (1983)

Neonatal Facial Expressions in Response to Different Qualities and Intensities of Gustatory Stimuli* JUDITH

R.

GANCHROW,

JACOB

E.

STEINER,

AND

MUNIF

DAHER

The Hebrew Universi~-Hadassah School of Dental Medicine

Facial expressions of 23 neonates were analyzed for specific features following oral stimulation with distilled water, 0.1 and 1.0 M sucrose, 0.15 and 0.25 M urea, and 0.0001 M quinine hydrochloride. Responses were videotaped and later decoded in a double-blind setting. While some features were present for all stimulations, other components were consistently associated with a specific taste quality. Within a quality, increasing the concentration elevated the incidence of features associated with that quality. Estimates of magnitude and hedonic tone conveyed by the total facial response to each stimulus suggested that the face was, within limits, an accurate reflection of stimulus quality and intensity. facial expression

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Facial expressions are among man's most efficient nonverbal communicational tools. Long before ethology became a separate discipline, Charles Darwin (1872/1965) suggested that displays in the oral and facial regions of both man and animals reflect fluctuations of affect or mood. Most sensory information gathered by man is evaluated not only with respect to its quality, intensity, and spatial dimensions, but also according to the hedonic tone it evokes (Pfaffmann, 1960). That is, behavioral responses to sensory stimuli may convey messages of "pleasure," "indifference," or "dissatisfaction" (e.g., Pfaffmann, Norgren, & Grill, 1977). Seventy-seven years ago, Sherrington (1906/1961) pointed out that stimulation of the "non-proficient" (contact) receptors, which stand in close relation to consummatory behaviors, are associated with strong affective tone. Gustatory stimuli are, therefore, primary vehicles for eliciting hedonic reactions, such as facial expression. The newborn infant, in the very first hours of extrauterine life, displays differential facial reactions to sweet, bitter, and sour tasting stimuli (Steiner, 1973, 1974, 1979). These responses conveyed to the observer feelings of pleasure, dislike, or disgust. It was concluded from these observations that the infant's ability to display facial expressions to gustatory stimuli was innate. The elimination of learning variables as being essential for the expression of the "gustofacial reflex" was * This study was conducted as part of a M.D. dissertation ofM. Daher. Some of the results reported here were included in a presentation by the senior author at the V. ECRO Minisymposium held in Jerusalem in November. 1981. Correspondence and requests for reprints should be addressed to J. R. Ganchrow. Department of Oral Biology. The Hebrew University-Hadassah School of Dental Medicine. P.O.B. 1172. Jerusalem, Israel.

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further based on studies of congenitally blind adolescents and mentally retarded individuals (Steiner, 1976, 1979). The latter two groups displayed reactions similar to those of the neonates. It has been demonstrated that clinical testing of infants born with developmental anomalies of the brain (anencephalics or hydroancephalics) can aid in the elucidation of brain stem function (Gamper, 1926; Monnier & Wili, 1947, 1953). Gustatory testing was not included in these studies. More recently (Steiner, 1973) gustatory stimulation has been shown to elicit the gustofacial response in such cases. Autopsies verified that the brainstems were intact, suggesting that this response is mediated in the region of the hindbrain. Expression of the gustofacial reflex is not limited to humans. Newborn rabbits and rats display this reaction (Ganchrow, Oppenheimer, & Steiner, 1979; Steiner, 1981) as well as adult rats (Grill & Norgren, 1978a). Further, taste reactions of decerebrate rats (Grill & Norgren, 1978b) were essentially the same as those of intact rats, again implying that the caudal brainstem is responsible for triggering these behaviors. In summary, differential facial displays to gustatory stimuli are innate, exhibited across several species, and dependent upon intrinsic coordination mechanisms of the brainstem. If it is accepted that the face is capable of showing distinctive expressions for several classes of gustatory stimuli, the question remains whether these expressions vary with stimulus intensity. Until recently, research on facial expression has focused primarily on grossly distinguishing pleasant and unpleasant emotions. However, Ekman, Friesen, and Ancoli (1980) directly addressed the question whether spontaneous facial behavior varied with the felt intensity of pleasant or unpleasant emotions and obtained positive correlations. It is known that increases in the concentration of gustatory stimuli are often associated with increases in pleasantness or unpleasantness as reported in human psychophysical studies (e.g., Moskowitz, 1977). Further, newborns are sensitive to changes in gustatory stimulus intensity (e.g., Crook, 1978). Thus, one might predict that the infant gustofacial reflex might be sensitive to changes in stimulus intensity. The present study was designed to test this hypothesis by scoring specific videotaped facial actions evoked by different concentrations of bitter and sweet stimuli in a double-blind setting. METHOD Fourteen male and nine female term-born human neonates (median weight 3.3 kg) were tested in the moming hours, shortly after delivery, in the Hadassah-University Hospital newborn nursery. All had been designated healthy and normal by the pediatric staff. Fourteen of these infants were tested before their first feeding, while 8 were examined within 3 hours of first exposure to breast or bottle. Babies were selected in a quiescent state and remained so during testing. Written consent was obtained from the parents, who were allowed to be present if they so desired. The taste stimuli tested included reagent grade aqueous solutions of. I and 1.0 M sucrose,. 15 and .25 M urea, and water. The low and high concentrations of each

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quality were roughly equated for intensity by adult judges prior to the experiment. Additionally, 18 of the 23 infants received .0001 M quinine hydrochloride. Sterile, bidistilled water was used as the solvent, the water stimulus, and for the water rinses presented between test trials. Room temperature (23 ± 2°C) fluids were delivered in .5 ml volumes intraorally via sterilized glass (or disposable plastic) graduated pipettes. The conditions for videotaping required that the Perspex crib, containing the lightly swaddled infant, be elevated about 35 ° at the head-end in order to face the camera (Sony black and white Vidicon). An auxilliary television screen was used to monitor conditions (e.g., focus, frontal view of face filling the screen) which were being videotaped on a Sony U-matic 3/4" VTR recorder using KCA-60 type cassettes. A highly sensitive microphone, placed next to the crib, recorded any infant vocalizations or noteworthy experimenter comments on the audio track of the tape. Natural room illumination was adequate for good recordings obviating the need for high intensity light sources which could create blinking or facial expressions not related to tasting. Prior to stimulus presentation, neonate identification was visually recorded as well as a 60-90 sec segment of the infant's resting face to familiarize the decoder with possible recurrent, spontaneous facial movements characterizing any particular infant. Next .5 ml water was given to rinse the mouth and to afford the decoder an estimate of baseline reactivity for each infant. Then the stimuli were presented in a random order, differing for every infant. The ensuing response was videotaped for at least 60 sec, continuing until facial actions ceased. Water rinses intervened between each stimulus delivery, and responses to these were not recorded. Occasionally a stimulus or a water rinse was repeated, but no baby received more than 8 ml fluid and most received 5.5 ml during a session. The whole procedure took about V_, hour per baby. All of the stimulus containers were precoded with numbers prior to the testing session. The corresponding number, printed on a white card, was placed in the video field, near the infant's head, during testing of that stimulus. Thus, neither those presenting the stimuli, nor the decoder, was aware which tastant was given on any trial. Decoding the facial behaviors was accomplished at a later date by tallying facial reaction components on a scoring sheet during repeated silent viewing of individual testing sessions. The scoring sheet contained a list of facial features based on agreement between lists provided the three decoders analyzing videotaped infant facial responses to bitter and sweet stimuli during a pilot study. One of these decoders (M.D.) was the final decoder, and he acquired expertise in behavioral analysis during these pilot sessions. For each coded stimulus presentation, two scoring sheets were provided. The first sheet listed 25 response components grouped according to head movements, eyes, nose, mouth, lips, tongue, and salivation (see legend, Figure 2). Because it is difficult to look and write at the same time, visual impressions were dictated into a tape recorder, and these verbalizations

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were immediately retrieved and tallied. The entire response, as well as individual segments, could be replayed as often as necessary to make a decision concerning any facial action. The second sheet was provided in order to score estimates of intensity and hedonic tone communicated by the overall facial response. Here the observer could make use of those features displayed as well as interpretations of magnitude, duration, and frequency of the response. Subtle cues related to arousal might also be taken into consideration. Estimates were scored along two 100 mm lines. For the hedonic estimates, the left end of the line was marked by the word "dislike" and the other by the word "like." The ends of the line for intensity estimates were polarized by the words " w e a k " and "strong." The vocalizations were examined early in the experiment and found to be practically nonexistent. The audio records were thus eliminated from further analysis. RESULTS Specific behavioral reactions to gustatory stimuli could be observed in all of the neonates examined. Examples of some of these facial features are presented in Figure 1. The resting face at the left may be compared with the response to sucrose in the top row, and the response to quinine in the bottom row. At a glance one can observe several of the characteristic components listed in the legend of Figure 2.,On the other hand, some feature similarities may also be observed (Compare Ic Above to At Rest). The percentage of babies expressing each feature relative to each stimulus is graphed in Figure 2. The order of feature presentation along all abscissae was arranged according to decreasing incidence of feature occurrence in response to 1.0 M sucrose. Overall, one can see that while responses to sucrose tend to cluster to the left side of the scale, the response distribution to quinine and urea is different and shifted to the right, peaking around features B (head turning) and S (lower lip in). Specific details will now be examined.

Response to Water The introduction of water into the oral cavity elicited a low incidence of fleeting movements associated with fluid consumption (e.g., licking [Q] and sucking [P], Figure 2) while general features of the resting face (e.g., eyes relaxed and closed [F] were maintained. When this distribution was compared to all the others, the highest Spearman rank correlation coefficients were obtained for the low concentrations of urea (r s = .29) and sucrose (rs = .33).

Response to Sucrose A clear resemblance between the components comprising reactions to both concentrations of sucrose is apparent in Figure 2. The Spearman rank correlation coefficient associated with these two distributions is r s = .87. Features Q through R (along the abscissa) are expressed with increasing frequency from water through. 1

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M sucrose to 1.0 M sucrose. Apparently Q (licking), P (sucking), and M (smiling) are the most distinguishing characteristics due to their frequent occurrence after sucrose stimulation. More descriptively, a " s w e e t " reaction is often seen as a slight parting of the lips (H) (see also Figure l a) followed by rapid, rhythmic licking of the upper lip evolving into vigorous sucking movements (Q, P) (see also Figure lb). This is sometimes followed by a slight smile (M).

Response to Urea and Quinine The reaction to bitter for all three stimuli tested is distributed in a set of characteristics quite different from that to sucrose or water. In Figure 2, features 1, and O through A are expressed by more and more babies comparing water responses to reactions t o . 15 M urea and .25 M urea, respectively. The response to quinine is similar to that for urea, but more features from the right side of the scale are recruited. The most frequently occurring characteristics are head turning (B), lower lip in (S), and wide open mouth (I) (see also Figure lc). The occurrence of any of features G through A, along the abscissa of Figure 2, was almost always associated with bitter stimuli, for example, closed mouth, corners down (N), repetitive lip pursing (U), open mouth, corners down (J) (see also Figure I b), and drooling (X). Response features to low and high concentrations were similar to each other (r s = .76), and to quinine (rs = .71 and .80, respectively). The correlation of responses to these bitter substances as compared to sucrose was quite low (e.g., Quinine-. 1 M sucrose, r~ = .04; Q u i n i n e - l . 0 M sucrose, r~ = .05).

Response Intensity The estimates for magnitudes of the gustofacial response are presented in Figure 3A. Water stimulation produced the least intense facial reaction. Low concentrations of each of the two gustatory qualities initiated facial reactions which were interpreted as slightly more intense than water (p < .05, Wilcoxon). Furthermore, responses to the high concentrations of sucrose and urea, as well as to quinine, differed significantly from reactions to the respective lower concentrations, as well as to water (p < .005, Wilcoxon).

Hedonic Reactions Estimates concerning the affect conveyed by the neonates' facial expressions are presented in Figure 3B. While water produced responses read as neutral in sign, sucrose evoked responses successively interpreted as expressing increasing pleasure as the concentration increased from .0 M through .1 M to 1.0 M. On the other hand, expressions in response to increasing concentrations of urea were evaluated as more and more unpleasant with quinine representing the most unpleasant stimulus. Hedonic estimates at all concentrations were significantly different from water; and within a stimulus class, the higher concentrations produced estimates significantly different from the lower concentrations, (p < .05, Sign-test, Siegel, 1956).

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DISCUSSION Earlier studies of the gustofacial reflex in infants focused primarily on the relationship between the stimulus quality and the quality of the response (e.g., Jacobs, Smutz, & Dubose, 1977; Steiner, 1973, 1974, 1979). Response quality in those studies refers to the overall muscular response as interpreted by the observer. It was suggested that a systematic analysis of the response components might lead to a better understanding of the communicative aspect of the gustofacial reflex in the framework of the mother-child interaction. Thus, the present investigation fractionated the total response into a catalogue of key expressions associated with bitter and sweet stimuli. When the responses of 23 infants were tallied on this catalogue, different sets of features were found to be most often associated with each particular quality, although there was some overlap (see Figure 2). Overlap would be expected since some facial movements accompany intake and swallowing. Intraoral tactile and thermal stimulation upon fluid presentation was a sufficient condition to trigger occasional licking movements, and to initiate the typical ingestion motion of the neonate, i.e., sucking. However, as sucrose was increased in intensity, more and more babies expressed these two features in addition to smiling. In fact, the effect of increasing the sucrose concentration was to increase the probability that any given baby would emit more facial features characterizing "sweet" (e.g., rolled tongue, closed moving mouth, etc.). Head posture and movements are also behaviors associated with feeding. A gentle raising and slight turning of the head can be associated with searching as observed in rooting (Prechtl, 1974). The appearance of "head turn" (component B, Figure 2) demonstrates that the same feature might be involved in both acceptance and rejection behavior. While B occurs at a low frequency for all stimuli, increasing the concentration of the bitter stimuli made this a dominant identifying feature. Head turning, in this instance, is probably more programmed as a defense reaction. Elimination of disturbing, rejected objects from the oral cavity can be achieved either by appropriate expulsion movements. These two mechanisms merge in movements denoting retching (Y) accompanied by drooling (X). These features practically never appear after sweet or water stimulation, but are not unusual after bitter stimulations. One of the best known facial expressions of aversion and disgust is a widely opened mouth with comers depressed and a flat, slightly protruded tongue (see Figure I, "bitter" response, b and c). Indeed, "gaping", and "open mouth, comers down" (Figure 2, K and J, respectively) were uniquely associated with quinine, while the occurrence of "wide open mouth" (1) increased in appearance as the urea concentration increased, and was present nearly 70% of the time for quinine. Other features unique to bitter stimuli were "raised head" (A), "repetitive lip pursing" (U), "closed mouth, comers down" (N), "quick blinks" (D), *'wrinkled nose" (G), and "lower lip in" (S), the latter feature being a very typical response. "Lip pursing" (O, also Figure lb) was characteristic of this bitter response.

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GANCHROW, STEINER,AND DAHER

Taken together, these expressions communicated information concerning the hedonic value of the stimulus. Facial reactions to low concentrations of sucrose (and urea) were judged to be more pleasant (or less pleasant) than water, even though the decoder did not know which stimulus had been presented. Increasing the concentration increased the separation of these estimates from water even more (see Figure 3). Thus, the hedonic value assigned to 1. M sucrose was highly positive and correspondingly negative for .25 M urea and quinine. The ability of a caretaker to read these emotions, expressed in the first year of infancy when verbal communication is minimal, may be important for the infant's welfare. It is known that substances described as "bitter" (e.g., quinine) are often poisonous (Schiffman & Erickson, 1971). Thus, if an infant picked up and began to orally explore a poisonous object, the facial expression could be the first sign of distress. Conversely, an expression emitting pleasure and satisfaction could reinforce and sustain the presentation of nutritious food. Human or mammalian perioral motor responses which differentiate between "acceptance" and "rejection" are not isolated phenomena, and they should be understood in a broader context. The motor response of single-celled organisms to attractive and repulsive chemicals was observed in the 19th century and labelled as positive and negative chemotaxis. This biological phenomenon has been reinvestigated by contemporary researchers (Adler & Tso, 1974; Hazelbauer, Engstroem, Harayama, & Koman, 1979; Macnab & Koshland, 1972). Differential motor responses of insects, in general, and their mouth organs, in particular, were also found to be guided by chemical cues, both in larval and adult life (Dethier, 1954; Schoonhoven, 1979), Among examples of motor responses reflecting hedonics of chemical stimuli in vertebrates, one could refer to studies on birds both during embryonic and adult phases of life. Here again the mouth area is involved in motion sequences indicating "acceptance" and "aversion." Gaping and beak clapping have been observed to be differential motor behaviors in chickens (Gentle, 1982; Vince, 1977). Not only food-related chemical stimuli, but also sex-attractants, may elicit oral-facial responses suggesting preference. Such coordinations were demonstrated by Dunbar (1977, 1978) in dogs responding to the odor of conspecific urine. Also, the neonate infant's face was found to reflect the hedonics of odors related (Steiner & Finnegan, 1975) and non-related to nutrients (MacFarlane, 1975; Schaal, Montagne, Hertling, Bolzoni, Moyse, & Quichon, 1980). In conclusion, the human gustofacial response is an innate response of the nervous system sensitive to changes in stimulus intensity. By the elicitation of this reflex with bitter and sweet stimuli, the basic features of the expressive facial movements can be brought to a display. A list of 25 motion components describing some components of these facial expressions was found to reflect distinct features conveying the message of acceptance, indifference, and aversion, respectively. REFERENCES Adler, J., & Tso, W. "Decision'-makingin bacteria: Chemotactic response of Escherichia coli to conflicting stimuli. Science, 1974, 184. 1292-1294.

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Crook, C. K. Taste perception in the newborn infant, lnfant Behavior & Development, 1978,/, 52-69. Darwin, C. The expression of the emotions in man and animals. London: John Murray, 1872. (Reprinted Chicago IL: University of Chicago Press, 1965.) Dethier, V. G. The physiology of olfaction in insects. Annals of the New York Academy of Science, 1954, 58, 139-157. Dunbar, I. F. Olfactory preference in dogs: The response of male and female beagles to conspecific odors. Behavioral Biology. 1977, 20, 417-418. Dunbar, I. F. Olfactory preferences in dogs: The response of male and female beagles to conspecific urine, Biology of Behaviour, 1978, 3. 723-786. Ekman, P., Friesen, W. V., & Ancoli, S. Facial signs of emotional experience. Journal of Personali~. and Social Psychology, 1980, 39, 1125-1134. Gamper, E. Bau und Leistungen eines menschlichen Mittelhirnwesens (Arhinencephalie mit EncephaIocoele) zugleich ein Beitrag zur Teratologie und Fasersystematik; 2. Klinischer Tell. Zeitschrift fiir gesamte Neurologie und Psychiatrie, 1926, 104. 49-120. Ganchrow, J. R., Oppenheimer, M., & Steiner, J. E. Behavioural displays to gustatory stimuli in newborn rabbit pups, Chemical Senses and Flavour, 1979, 4, 49-61. Gentle, M. J. Oral behaviour in response to oral stimulation in Gallus domesticus. In J. E. Steiner & J. R. Ganchrow (Eds.), The determination of behaviour by chemical stimuli (V). ECRO-Minisymposium. London: Information Retrieval, 1982. Grill, H. J., & Norgren, R. The taste reactivity test. I. Mimetic response to gustatory stimuli in neurologically normal rats. Brain Research, 1978, 143. 263-269. (a) Grill, H. J., & Norgren, R. The taste reactivity test. II. Mimetic responses to gustatory stimuli in chronic thalamic and chronic decerebrate rats. Brain Research, 1978, 143. 281-297. (b) Hazelbauer, G. L., Engstroem, P., Harayama, S., & Koman, A. Preference behaviour in Escherichia coli: Involvement of both, receptors and transducers. In J. H. A. Kroeze (Ed.), Preference behaviour and chemoreception (111). ECRO-Minisymposium. London: Information Retrieval, 1979. Jacobs, H. L., Smutz, E. R.. & DuBose, C. N. Comparative observations on the ontogeny of taste preference. In J. M. Weiffenbach (Ed.). Taste and development: The genesis of sweet preference. Bethesda, MD: U.S. Dept. of Health, Education. and Welfare, 1977. MacFarlane, A. Olfaction in development of social preference in the human neonate. In R. Porter & M. O'Conner (Eds.). Symposium on the parent-infant relationship. Ciba Foundation Symposium, 33. Amsterdam: Elsevier, 1975. Macnab, R. M., & Koshland, D. E., Jr. The gradient sensing mechanism in bacterial chemotaxis. Proceedings of the National Academy of Science (U.S.A.), 1972, 69, 2509-2519. Monnier, M., & Will, H. Die integrative Tiitigkeit des Nervensystems beim bulbospinalen Anencephalen. (Rautenhirnwesen). Annales Pediatrici, 1947, 169, 289-308. Monnier. M., & Wili, H. Die integrative T~itigkeit des Nervensystems beim mesorhombo-spinalen Anencephalus. Monatschr(ft J~ir Psychiatrie und Neurologie. 1953, 126. 239-273. Moskowitz, H. R. Intensity and hedonic functions for chemosensory stimuli. In M. R. Kare & D. Mailer (Eds.), Chemical senses and nutrition. New York: Academic Press, 1977. Pfaffmann. C. The pleasure of sensation. Psychological Review, 1960, 67. 253-268. Pfaffmann, C.. Norgren, R.. & Grill, H. Sensory affect and motivation. Annals of the New York Academy of Science. 1977. 290. 18-34. Prechtl, H. F. R. The behavioral states of the newborn infant. Brah~ Research. 1974, 76, 185212. Schaal, B., Montange, H.. Hertling. E., Bolzoni, D., Moyse. A., & Quichon, R. Les stimulations olfactives dens les relations entre I'enfant et la m/:re. Annales de Biologie Animale. Biochemie, Biophysique. 1980, 20. 843-858. Schiffman. S. S., & Erickson, R. P. A psychophysical model for gustatory quality. Physiology & Behavior. 1971, 7, 617-633. Sehoonhoven, L. M. What is 'preference behaviour' in food selection by invertebrates? In J. H. A.

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Kroeze (Ed.), Preference behaviour and chemoreception (III). ECRO-Minisymposium. London: Information Retrieval, 1979. Sherrington, C. The integrative action of the nervous system. New Haven, CT: Yale University Press, 1906. (Reprinted New Haven, CT: Yale University Press, 1961.) Siegel, S. Nonparametric statistics for the behavioral sciences. New York: McGraw-Hill, 1956. Steiner, J. E. The gustofacial response: Observation on normal and anencephalic newborn infants. In J. F. Bosma (Ed.), Fourth symposium on oral sensation and perception. Bethesda, MD: U.S. Department of Health, Education, and Welfare, 1973. Steiner, J. E. Innate discriminative human facial expressions to taste and smell stimuli. Annals of the New York Academy of Science, 1974, 237, 229-233. Steiner, J. E. Further observations on sensory-motor coordinations induced by gustatory and olfactory stimuli. Israel Journal of Medical Sciences, 1976, 13, 545. Steiner, J. E. Human facial expressions in response to taste and smell stimulation. In H. Reese & L. P. Lipsitt (Eds.), Advances in child development and behavior. (Vol. 13). New York: Academic Press, 1979. Steiner, J. E. Behavioural and physiological responses to taste and odour stimuli. In Y. Kawamura (Ed.), Oral-facial sensory and motor functions. International Symposium on Oral Physiology. Tokyo: Quintessence Publishing Co., 1981. Steiner, J. E., & Finnegan, L. Innate discriminative facial expressions to food-related odors. Israel Journal of Medical Sciences, 1975, 11, 858. Vince, M. A. Taste sensitivity in the embryo of the domestic fowl. Animal Behaviour, 1977, 25, 797-805.

14 May 1981; Revised 1 February 1982 I[11