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Magnitude estimation of warmth in children
J. therm. Biol. Vol. 13, No. 2, pp. 85-88, 1988 Printed in Great Britain. All rights reserved
0306-4565/88 $3.00+0.00 Copyright © 1988PergamonPress plc
M A G N I T U D E ESTIMATION OF W A R M T H IN C H I L D R E N ROBERTO REFINETTI* Institute of Psychology, University of $5.o Paulo, 05508 S~.o Paulo, Brazil (Received I September 1987; accepted in revised form 14 November 1987) Abstract--1. Children from 3 to 18 years of age were asked to estimate the magnitude of the warmth sensation evoked by a metal bar whose temperature ranged from 33 to 42°C. 2. The exponent of the power function relating perceptual magnitude to stimulus magnitude was lower for children under 8 years of age (,8 ~ 0.40) than for older children (8 "~0.85). Exponents for brightness estimation were similar for all children. 3. These results suggest a developmental change in the warmth sense during the first 8 years of life. Key Word Index--Cross-modal matching; magnitude estimation; child; sensory development; temperature.
could be easily grasped by the child. Water maintained at 22°C was pumped to the stimulator after passing through a heat exchanger immersed in a 50°C water bath. Variations in stimulator temperature were obtained by varying the flow rate in the system, which was accomplished by varying the power to the pump with a commercial dimmer. A small red light on the stimulator frame served to signal the beginning of each trial. The experiment was fully controlled by a TRS-80 Model 4D microcomputer (Tandy Corporation, Fort Worth, Tex.) and an A-BUS interface system (Alpha Products, Darien, Conn.). The interface system included an analog output to control the dimmer, a digital output for the light signal, two digital inputs connected to tempory switches (used for yes/no responses), and two analog inputs connected to a slide potentiometer (used for the estimation of stimulus magnitude) and to a thermistor attached to the stimulator. Before each session, the thermistor was calibrated (resolution = 0.1 °C) in a stirred water bath with a BAT-12 thermocouple meter and IT-23 probe (Sensortek, Clifton, N.J.). Temperature control of the stimulator was accurate to 0.2°C.
INTRODUCTION Studies on perceptual development in children have demonstrated significant changes in the perception of visual, auditory, and haptic stimuli during the first years of life (see Piaget, 1969; Sinclair, 1981; Woolsey et al., 1981). Regarding the thermal senses, several psychophysical studies have been conducted in adults (Hensel, 1981; Stevens, 1983) but no study has directly addressed the question of development during childhood. Developmental thermal physiologists have concentrated their efforts on the study of thermoregulatory responses rather than on thermal sensations (Briick, 1978). The present study was designed to investigate the existence of developmental changes in the warmth sense in children from 3 to 18 years of age. The ability to estimate the magnitude of a warm stimulus (Stevens and Stevens, 1960) was used as an index of perceptual development. MATERIALS AND METHODS
Subjects Thirty-eight children of both sexes between 3 and 18 years of age were used as subjects. They were all normal children as judged from the school and medical records provided by their parents. Parental consent to participate in the experiment was secured for all subjects. The children and their parents were informed about the general nature of the experiment, but details about the experimental procedure were not disclosed until the end of the study.
Procedure Subjects were asked not to engage in vigorous physical activity for at least two hours before the experiment. Upon their arrival in the laboratory, they were taken to the experimental room and asked to sit quietly for 15 min. At the end of this period, measurements were made of sublingual temperature, heart rate, and palmar temperature of the left hand. The experimental session proper was then initiated. It consisted of two parts: threshold determination and magnitude estimation (or, more exactly, cross-modal matching of a judgmental continuum and the target continuum). Instructions for Part 1 (determination of an approximate warmth threshold) were given as follows: "When this little red light is turned on, place your left hand on this bar and hold it firmly. The bar will be either cold or warm. If it is cold, press this [the left]
Apparatus All sessions were conducted in a thermostatically controlled room set to 25°C. The thermal stimulator, located on a table in the center of the room, consisted of a thin-wall brass tube (26 mm diameter, 15 cm length) perfused with water at different temperatures. The tube was housed in a Plexiglas frame so that it *Present address: Institute of Environmental Stress, University of California, Santa Barbara, CA 93106, U.S.A. 85
86
ROBERTO REFINETTI
switch with your right hand; if it is warm, press this [the right] switch. Please respond as soon as you have the thermal sensation; if the sensation is not clear at once, press any of the switches at random. After pressing (and releasing) the switch, remove your left hand from the bar and wait for the red light to be turned on again." Children under 5 years of age were allowed to have an adult companion with them (mother, baby sitter, etc.) if they so wished. The companion was instructed to watch for the red light and prompt the child to respond, but not to touch the stimulator or interfere in any way with the child's introspective report. The experimenter observed the room through a one-way mirror to certify that the subject and his companion were behaving in accordance with the instructions. After a few training trials, data recording was initiated. Temperatures between 30 and 36°C (at I°C steps) were randomly presented by the method of constant stimuli (Graham, 1950). Thirty-five stimuli were presented in a session. The interval between two consecutive stimuli depended on the latency of the response, but was never shorter than 40 s. Stimulus duration was also dependent on the subject, as each trial was terminated when the child pressed the switch and removed the hand. This variability in exposure time is unlikely to affect thermal sensation significantly because temporal summation occurs only for very short (<1 s) stimuli (Marks and Stevens, 1973b) and adaptation takes several minutes (Kenshalo and Scott, 1966). If consistent differences in exposure time between adults and children existed, they were very small and could not be observed by the experimenter. After a 10 min interruption, during which candies were offered to the child, instructions were given for the second part of the session (magnitude estimation of warmth), as follows: "When this little red light is turned on, place your left hand on the bar and hold it, as you have been doing so far. The bar will always be warm. If it is too warm, move this knob up [experimenter shows the slide potentiometer], like this [experimenter moves the knob]. If it is not warm at all, move the knob down, like this. If it is a little warmer, move the knob up a little, like this. If it is even warmer, move it further up. Thus, the warmer the bar, the higher the knob. After you have decided where to place the knob, remove your left hand from the bar, move the knob with your fight hand, and press this switch [only one switch was used in Part 2]. Then, wait for the light to be turned on again." For children under 5 years of age, the companion was
instructed to watch for the red light, prompt the child to move the knob, and press the switch. Training trials with extreme temperatures (33 and 42°C) were conducted in an attempt to prevent inadvertent assignments of maximum scores to submaximal stimuli later on during the session. The subjects were explicitly informed that they were experiencing the lowest and highest levels of warmth. Data recording was then initiated. Temperatures between 33 and 42°C (at I°C steps) were presented by the method of constant stimuli. Twenty stimuli were presented in a session, in intervals of no less than 40 s. Half of the subjects were also tested for brightness estimation, as a control procedure. Equipment and procedure were the same as in Part 2 of the main experiment, except that a 60W tungsten bulb replaced the thermal stimulator. Illuminance was varied from 0 to 1200 Ix at steps of approximately 120 Ix. Brightness estimation preceded warmth estimation for some subjects and followed it for the others. RESULTS
Mean body temperature, palmar skin temperature, and heart rate at the beginning of the session are shown in Table 1. As expected, younger children had higher heart rates. They also had slightly lower body temperature, which is probably just an artifact due to the difficulty of placing the probe properly under the young child's tongue. Palmar skin temperature was less age-related and correlated poorly with core temperature: r = 0.24, P > 0.10. All subjects were able to judge the thermal stimuli in terms of warm and cold (Part 1). The warmth threshold was calculated as the intersection of the cold and warm curves (that is, threshold was defined as the neutral-sensation point where equal percentages of responses of warm and cold are obtained). Threshold as a function of age for individual subjects is shown in Fig. 1. The effect of age on threshold was tested by the Kruskal-Wallis test for eight age classes (3-4, 5~5, . . . , 17-18 years of age) and found not to be significant [H(7)= 10.50, P >0.10]. Also, threshold temperature correlated poorly with initial palmar skin temperature: r = 0.26, P > 0.10. Six out of 38 children were unable to perform the magnitude-estimation task (Part 2). Four of these six children were probably too young to fully understand the task (ages: 2.9, 3.0, 3.5, and 4.1 years). The other two, however, were much older (6.3 and 8.6 years of
Table 1. Mean baseline measurements of oral temperature (Tb), palmar skin temperature (T~), and heart rate (HR) for subjects of different ages Years of age
3~4
5~o
7-8
9-10
11-12
13-14
15-16
17-18
Tb ( C )
M SE
36.0 0.2
36.5 0.3
36.8 0.2
36.5 0.4
36.7 0.2
36.7 0.4
36.8 0.1
37.0 0.1
T~ ('C)
M SE
33.3 0.2
33.1 0.6
33.9 0.3
33.7 0.5
34.3 0.5
32.6 0.5
33.9 0.2
34.3 0.3
105 5
95 3
90 7
92 2
93 4
96 6
81 1
81 4
8
4
4
4
4
4
4
6
H R (min ~) Sample size
M SE
Thermal psychophysics 1.2
36-
"o
34 - •
II
Qo. O~
$
~ E
87
•
32--••
•
•
ee
•o
•
•
~
30 "
I
I
I
I
I
3
7
11
15
19
Years of age
0.4
ITI I
0.0
I
I
3
7
11 Y e a r s of age
I
I
15
19
Fig. 1. Threshold for warmth sensation as a function of age. (Each point corresponds to one subject.)
Fig. 3. Warmth-estimate exponent as a function of age. (Bars show mean + standard error.)
age) and there is no apparent reason for their erratic reports (their estimates were randomly related to stimulus temperature). Magnitude estimation data from two representative successful subjects are shown in Fig. 2. In each of the four graphs, the diagonal line indicates linear relationship between perceptual magnitude and stimulus magnitude from threshold to maximal warmth (the warmth threshold is at about 33°C and the pain threshold at 45°C). The estimates of stimulus magnitude, as indicated by the location of the potentiometer knob, were converted into grades in a linear scale from 1 to 10 by means of a simple algorithm at data-acquisition time. Regarding the warmth sense (Fig. 2a), the 4-year-old child moderately overestimated temperatures in the 34-37°C range and markedly in the 37-42°C range. The 18-year-old subject moderately overestimated temperatures in the 39-42°C range but was much more accurate at lower temperatures. Although the younger and older children overestimated mid and high values in the visual sense too (Fig. 2b), the difference between the two subjects was smaller. The psychophysical law for magnitude estimation (S. S. Stevens, 1970) can be written as:
function of age in the present experiment. There is a slight but significant effect of age on/3: H(7) = 15.03, P < 0.05. Apparently, fl increases with age up to 7-8 years and then stabilizes at about 0.85. Values of fl for brightness estimation oscillated around 0.35 independently of age.
= k(~
- ¢0)C
where ~b is perceptual magnitude, q~0 is stimulus magnitude at threshold, ¢ is actual stimulus magnitude, fl is the exponent of the power function, and k is a constant. Figure 3 shows the exponent fl as a
L." 3 j&=//
i, 33
I
37
",". Age4
41
Temperature (oc)
~W I A.M;
l~ 0
I 560
I 1120
I L L u m i n a n c e (Lux)
Fig. 2. Magnitude estimation of warmth (a) and brightness (b) by two subjects.
DISCUSSION
The results from Part I are consistent with previous research showing no change in the warmth threshold during development (Gray et al., 1982). The ease with which young children discriminated cold from warmth was not accompanied, however, by the ability to estimate the magnitude of a warm stimulus. A few children were unable to perform the magnitude estimation task and children under 8 years of age consistently overestimated temperatures in the 37-42°C range. This is reflected in the lower exponents for young children in Fig. 3 (but see below). Performance in the brightness estimation task was less age-dependent. Also, previous studies have shown that, although few children between 4 and 8 years of age can use the ratio properties of numbers in a matching situation, they are able to estimate stimulus magnitude by cross-modal matching with more concrete judgmental continua (Siegel and McBurney, 1970; Teghtsoonian, 1980). This suggests that the perceptual differences in the warmth sense found in this study are due to specific developmental differences in the warmth sense rather than to a general developmental difference in sensory-motor or conceptual organization. Further studies would be necessary to decide whether this development of temperature perception results from maturation, learning, or both. The values of/? found in this experiment should not be considered in absolute terms. It is very difficult to determine the best way to calculate ft. Because young children strongly overestimate temperatures above 36°C, calculations of fl might consider only the 33-36°C range. In this case, the thermal fl for subject A.M. in Fig. 2 would be 1.20, which is extremely higher than the value of 0.42 calculated for the whole 33-42°C range. But, since young children do overestimate more than adults, it would be incorrect to omit the data from the 37-42°C range. Naturally, although the values of fl used here allow a comparison among ages (e.g. Fig. 3), they are not good
88
ROBERTO REFINETTI
Table 2. Literature data on magnitude estimation of warmth in adults Authors Figure cm2 s /~ rL rN
Graham C. H. (1950) Behavior, perception and the psychophysical methods. Psychol. Rev. 57, 108-120. Gray L., Stevens J. C. and Marks L. E. (1982) Thermal stimulus thresholds: sources of variability. Physiol. Behav. Stevens and Marks (1971) 2 4 3 0.44 0.92 0.99 29, 355-360. Herget et al. (1941) 4 15 2 0.61 0.97 0.98 Stevens et al. (1974) 5 200 3 0.65 1.00 0.99* Hensel H. (1981) Thermoreception and Temperature Regulation. Academic Press, London. Marks et al. (1976) 3 I1 2 0.68 0.99 1.00 Herget C. M., Granath L. P. and Hardy J. D. (1941). Stevens et al. (1974) 9 22 3 0.78 0.98 0.99 Thermal sensation and discrimination in relation to inMolinari et al. (1977) 4 7 12 0.93 1.00 1.00 Stevens and Marks (1971) 7 127 3 0.95 1.00 1.00 tensity of stimulus. Am. J. Physiol. 134, 6454555. Marks and Stevens (1973a) 1 22 1/2 1.02 0.98 0.99 Kenshalo D. R. and Scott H. A. Jr (1966) Temporal course Stevens et al. (1974) 5 10 3 1.04 1.00 1.00 of thermal adaptation. Science 151, 1095 1096. Marks and Stevens (1973b) 7 22 6 1.06 1.00 0.99* Marks L. E. and Stevens J. C. (1973a) Spatial summation Marks and Stevens (1973a) 4 l0 3 1.07 1.00 1.00 of warmth. Influence of duration and configuration of the Stevens and Stevens (1960) 2 7 3 1.59 0.99 0.96* stimulus. Am. J. Psychol. 86, 251-267. The data wereobtained from the figuresindicatedfor each paper and Marks L. E. and Stevens J. C. (1973b) Temporal summation interpolated by the least-squares method. Stimulus size (cm2) related to the nature of the proximal stimulus for the and duration (s), power-function exponent (fl), and linearwarmth sense. Percept. Psychophys. 14, 570-576. correlation coefficientsfor log-log data (rL) and natural data (rN) are shown. All correlation coefficientsare significantat the Marks L. E., Stevens J. C. and Tepper S. J. (1976) Interaction of spatial and temporal summation in the warmth 0.01 level or better. Asterisksshow the cases where rNis smaller sense. Sensor)' Processes 1, 87 98. then r L. Molinari H. H., Greenspan J. D. and Kenshalo D. R. (1977) The effects of rate of temperature change and adapting indices for calculating perceptual magnitude from temperature on thermal sensitivity. Sensory Processes I, stimulus magnitude. It should be noticed, in this 354-362. connection, that the exact value o f fl for w a r m t h Piaget J. (1969) The Mechanisms o f Perception (translated estimation remains controversial even in adults. As by Seagrim N. G.). Basic Books, New York. can be seen in Table 2, previous studies in adults have Siegel A. W. and McBurney D. H. (1970) Estimation of line found exponents from 0.44 to 1.59. A l t h o u g h the length and number: a developmental study. J. exp. Child Psychol. 10, 170-180. value o f fl is related to stimulus size (Stevens and Marks, 1971) and d u r a t i o n (Marks and Stevens, Sinclair D. (1981) Mechanisms o f Cutaneous Sensation. Oxford University Press, Oxford. 1973b) within individual studies, the different exp o n e n t s s h o w n in Table 2 are clearly not related to Stevens J. C. (1983) Thermal sensation: infrared and microwaves. In Microwaves and Thermoregulation (Edited by these two parameters. There is no a p p a r e n t explaAdair E. R.), pp. 191 201. Academic Press, New York. nation for the large variability in the results o b t a i n e d Stevens J. C. and Stevens S. S. (1960) Warmth and cold: in different studies. Practice tends to m o v e fl to 1.0, dynamics of sensory intensity. J. exp. Psychol. 60, larger values being reduced and smaller values being 183-192. increased (unpublished observations), but all subjects Stevens J. C. and Marks L. E. (1971) Spatial summation and the dynamics of warmth sensation. Percept. P~ychophys. in the studies cited above had extensive training 9, 391 398. before the experimental sessions. A curious detail in Table 2 is that in only 3 out o f Stevens J. C., Marks L. E. and Simonson D. C. (1974) Regional sensitivity and spatial summation in the warmth 12 cases is r N smaller than r L. This means that in m o s t sense. Physiol. Behav. 13, 825-836. cases the relationship between perceptual intensity Stevens S. S. (1970) Neural events and the psychophysical and stimulus magnitude is n o t better represented by law. Science 170, 1043-1050. a power function than by a linear function. In the Teghtsoonian M. (1980) Children's scales of length and present study, only 10 out o f 32 data sets were loudness: a developmental application of cross-modal represented better by a power function t h a n by a matching. J. exp. Child Psychol. 30, 290 -~307. Woolsey T. A., Durham D., Harris R. M., Simons D. J. and linear function. Valentino K. L. (1981) Somatosensory development. In REFERENCES Development o f Perception (Edited by Aslin R. N., Alberts J. R. and Petersen M. R.), Vol. 1, pp. 259--292. Academic Briick K. (1978) Heat production and temperature reguPress, New York. lation. In Perinatal Physiology (Edited by Stave U.), pp. 455~,98. Plenum Medical, New York.
0306-4565/88 $3.00+0.00 Copyright © 1988PergamonPress plc
M A G N I T U D E ESTIMATION OF W A R M T H IN C H I L D R E N ROBERTO REFINETTI* Institute of Psychology, University of $5.o Paulo, 05508 S~.o Paulo, Brazil (Received I September 1987; accepted in revised form 14 November 1987) Abstract--1. Children from 3 to 18 years of age were asked to estimate the magnitude of the warmth sensation evoked by a metal bar whose temperature ranged from 33 to 42°C. 2. The exponent of the power function relating perceptual magnitude to stimulus magnitude was lower for children under 8 years of age (,8 ~ 0.40) than for older children (8 "~0.85). Exponents for brightness estimation were similar for all children. 3. These results suggest a developmental change in the warmth sense during the first 8 years of life. Key Word Index--Cross-modal matching; magnitude estimation; child; sensory development; temperature.
could be easily grasped by the child. Water maintained at 22°C was pumped to the stimulator after passing through a heat exchanger immersed in a 50°C water bath. Variations in stimulator temperature were obtained by varying the flow rate in the system, which was accomplished by varying the power to the pump with a commercial dimmer. A small red light on the stimulator frame served to signal the beginning of each trial. The experiment was fully controlled by a TRS-80 Model 4D microcomputer (Tandy Corporation, Fort Worth, Tex.) and an A-BUS interface system (Alpha Products, Darien, Conn.). The interface system included an analog output to control the dimmer, a digital output for the light signal, two digital inputs connected to tempory switches (used for yes/no responses), and two analog inputs connected to a slide potentiometer (used for the estimation of stimulus magnitude) and to a thermistor attached to the stimulator. Before each session, the thermistor was calibrated (resolution = 0.1 °C) in a stirred water bath with a BAT-12 thermocouple meter and IT-23 probe (Sensortek, Clifton, N.J.). Temperature control of the stimulator was accurate to 0.2°C.
INTRODUCTION Studies on perceptual development in children have demonstrated significant changes in the perception of visual, auditory, and haptic stimuli during the first years of life (see Piaget, 1969; Sinclair, 1981; Woolsey et al., 1981). Regarding the thermal senses, several psychophysical studies have been conducted in adults (Hensel, 1981; Stevens, 1983) but no study has directly addressed the question of development during childhood. Developmental thermal physiologists have concentrated their efforts on the study of thermoregulatory responses rather than on thermal sensations (Briick, 1978). The present study was designed to investigate the existence of developmental changes in the warmth sense in children from 3 to 18 years of age. The ability to estimate the magnitude of a warm stimulus (Stevens and Stevens, 1960) was used as an index of perceptual development. MATERIALS AND METHODS
Subjects Thirty-eight children of both sexes between 3 and 18 years of age were used as subjects. They were all normal children as judged from the school and medical records provided by their parents. Parental consent to participate in the experiment was secured for all subjects. The children and their parents were informed about the general nature of the experiment, but details about the experimental procedure were not disclosed until the end of the study.
Procedure Subjects were asked not to engage in vigorous physical activity for at least two hours before the experiment. Upon their arrival in the laboratory, they were taken to the experimental room and asked to sit quietly for 15 min. At the end of this period, measurements were made of sublingual temperature, heart rate, and palmar temperature of the left hand. The experimental session proper was then initiated. It consisted of two parts: threshold determination and magnitude estimation (or, more exactly, cross-modal matching of a judgmental continuum and the target continuum). Instructions for Part 1 (determination of an approximate warmth threshold) were given as follows: "When this little red light is turned on, place your left hand on this bar and hold it firmly. The bar will be either cold or warm. If it is cold, press this [the left]
Apparatus All sessions were conducted in a thermostatically controlled room set to 25°C. The thermal stimulator, located on a table in the center of the room, consisted of a thin-wall brass tube (26 mm diameter, 15 cm length) perfused with water at different temperatures. The tube was housed in a Plexiglas frame so that it *Present address: Institute of Environmental Stress, University of California, Santa Barbara, CA 93106, U.S.A. 85
86
ROBERTO REFINETTI
switch with your right hand; if it is warm, press this [the right] switch. Please respond as soon as you have the thermal sensation; if the sensation is not clear at once, press any of the switches at random. After pressing (and releasing) the switch, remove your left hand from the bar and wait for the red light to be turned on again." Children under 5 years of age were allowed to have an adult companion with them (mother, baby sitter, etc.) if they so wished. The companion was instructed to watch for the red light and prompt the child to respond, but not to touch the stimulator or interfere in any way with the child's introspective report. The experimenter observed the room through a one-way mirror to certify that the subject and his companion were behaving in accordance with the instructions. After a few training trials, data recording was initiated. Temperatures between 30 and 36°C (at I°C steps) were randomly presented by the method of constant stimuli (Graham, 1950). Thirty-five stimuli were presented in a session. The interval between two consecutive stimuli depended on the latency of the response, but was never shorter than 40 s. Stimulus duration was also dependent on the subject, as each trial was terminated when the child pressed the switch and removed the hand. This variability in exposure time is unlikely to affect thermal sensation significantly because temporal summation occurs only for very short (<1 s) stimuli (Marks and Stevens, 1973b) and adaptation takes several minutes (Kenshalo and Scott, 1966). If consistent differences in exposure time between adults and children existed, they were very small and could not be observed by the experimenter. After a 10 min interruption, during which candies were offered to the child, instructions were given for the second part of the session (magnitude estimation of warmth), as follows: "When this little red light is turned on, place your left hand on the bar and hold it, as you have been doing so far. The bar will always be warm. If it is too warm, move this knob up [experimenter shows the slide potentiometer], like this [experimenter moves the knob]. If it is not warm at all, move the knob down, like this. If it is a little warmer, move the knob up a little, like this. If it is even warmer, move it further up. Thus, the warmer the bar, the higher the knob. After you have decided where to place the knob, remove your left hand from the bar, move the knob with your fight hand, and press this switch [only one switch was used in Part 2]. Then, wait for the light to be turned on again." For children under 5 years of age, the companion was
instructed to watch for the red light, prompt the child to move the knob, and press the switch. Training trials with extreme temperatures (33 and 42°C) were conducted in an attempt to prevent inadvertent assignments of maximum scores to submaximal stimuli later on during the session. The subjects were explicitly informed that they were experiencing the lowest and highest levels of warmth. Data recording was then initiated. Temperatures between 33 and 42°C (at I°C steps) were presented by the method of constant stimuli. Twenty stimuli were presented in a session, in intervals of no less than 40 s. Half of the subjects were also tested for brightness estimation, as a control procedure. Equipment and procedure were the same as in Part 2 of the main experiment, except that a 60W tungsten bulb replaced the thermal stimulator. Illuminance was varied from 0 to 1200 Ix at steps of approximately 120 Ix. Brightness estimation preceded warmth estimation for some subjects and followed it for the others. RESULTS
Mean body temperature, palmar skin temperature, and heart rate at the beginning of the session are shown in Table 1. As expected, younger children had higher heart rates. They also had slightly lower body temperature, which is probably just an artifact due to the difficulty of placing the probe properly under the young child's tongue. Palmar skin temperature was less age-related and correlated poorly with core temperature: r = 0.24, P > 0.10. All subjects were able to judge the thermal stimuli in terms of warm and cold (Part 1). The warmth threshold was calculated as the intersection of the cold and warm curves (that is, threshold was defined as the neutral-sensation point where equal percentages of responses of warm and cold are obtained). Threshold as a function of age for individual subjects is shown in Fig. 1. The effect of age on threshold was tested by the Kruskal-Wallis test for eight age classes (3-4, 5~5, . . . , 17-18 years of age) and found not to be significant [H(7)= 10.50, P >0.10]. Also, threshold temperature correlated poorly with initial palmar skin temperature: r = 0.26, P > 0.10. Six out of 38 children were unable to perform the magnitude-estimation task (Part 2). Four of these six children were probably too young to fully understand the task (ages: 2.9, 3.0, 3.5, and 4.1 years). The other two, however, were much older (6.3 and 8.6 years of
Table 1. Mean baseline measurements of oral temperature (Tb), palmar skin temperature (T~), and heart rate (HR) for subjects of different ages Years of age
3~4
5~o
7-8
9-10
11-12
13-14
15-16
17-18
Tb ( C )
M SE
36.0 0.2
36.5 0.3
36.8 0.2
36.5 0.4
36.7 0.2
36.7 0.4
36.8 0.1
37.0 0.1
T~ ('C)
M SE
33.3 0.2
33.1 0.6
33.9 0.3
33.7 0.5
34.3 0.5
32.6 0.5
33.9 0.2
34.3 0.3
105 5
95 3
90 7
92 2
93 4
96 6
81 1
81 4
8
4
4
4
4
4
4
6
H R (min ~) Sample size
M SE
Thermal psychophysics 1.2
36-
"o
34 - •
II
Qo. O~
$
~ E
87
•
32--••
•
•
ee
•o
•
•
~
30 "
I
I
I
I
I
3
7
11
15
19
Years of age
0.4
ITI I
0.0
I
I
3
7
11 Y e a r s of age
I
I
15
19
Fig. 1. Threshold for warmth sensation as a function of age. (Each point corresponds to one subject.)
Fig. 3. Warmth-estimate exponent as a function of age. (Bars show mean + standard error.)
age) and there is no apparent reason for their erratic reports (their estimates were randomly related to stimulus temperature). Magnitude estimation data from two representative successful subjects are shown in Fig. 2. In each of the four graphs, the diagonal line indicates linear relationship between perceptual magnitude and stimulus magnitude from threshold to maximal warmth (the warmth threshold is at about 33°C and the pain threshold at 45°C). The estimates of stimulus magnitude, as indicated by the location of the potentiometer knob, were converted into grades in a linear scale from 1 to 10 by means of a simple algorithm at data-acquisition time. Regarding the warmth sense (Fig. 2a), the 4-year-old child moderately overestimated temperatures in the 34-37°C range and markedly in the 37-42°C range. The 18-year-old subject moderately overestimated temperatures in the 39-42°C range but was much more accurate at lower temperatures. Although the younger and older children overestimated mid and high values in the visual sense too (Fig. 2b), the difference between the two subjects was smaller. The psychophysical law for magnitude estimation (S. S. Stevens, 1970) can be written as:
function of age in the present experiment. There is a slight but significant effect of age on/3: H(7) = 15.03, P < 0.05. Apparently, fl increases with age up to 7-8 years and then stabilizes at about 0.85. Values of fl for brightness estimation oscillated around 0.35 independently of age.
= k(~
- ¢0)C
where ~b is perceptual magnitude, q~0 is stimulus magnitude at threshold, ¢ is actual stimulus magnitude, fl is the exponent of the power function, and k is a constant. Figure 3 shows the exponent fl as a
L." 3 j&=//
i, 33
I
37
",". Age4
41
Temperature (oc)
~W I A.M;
l~ 0
I 560
I 1120
I L L u m i n a n c e (Lux)
Fig. 2. Magnitude estimation of warmth (a) and brightness (b) by two subjects.
DISCUSSION
The results from Part I are consistent with previous research showing no change in the warmth threshold during development (Gray et al., 1982). The ease with which young children discriminated cold from warmth was not accompanied, however, by the ability to estimate the magnitude of a warm stimulus. A few children were unable to perform the magnitude estimation task and children under 8 years of age consistently overestimated temperatures in the 37-42°C range. This is reflected in the lower exponents for young children in Fig. 3 (but see below). Performance in the brightness estimation task was less age-dependent. Also, previous studies have shown that, although few children between 4 and 8 years of age can use the ratio properties of numbers in a matching situation, they are able to estimate stimulus magnitude by cross-modal matching with more concrete judgmental continua (Siegel and McBurney, 1970; Teghtsoonian, 1980). This suggests that the perceptual differences in the warmth sense found in this study are due to specific developmental differences in the warmth sense rather than to a general developmental difference in sensory-motor or conceptual organization. Further studies would be necessary to decide whether this development of temperature perception results from maturation, learning, or both. The values of/? found in this experiment should not be considered in absolute terms. It is very difficult to determine the best way to calculate ft. Because young children strongly overestimate temperatures above 36°C, calculations of fl might consider only the 33-36°C range. In this case, the thermal fl for subject A.M. in Fig. 2 would be 1.20, which is extremely higher than the value of 0.42 calculated for the whole 33-42°C range. But, since young children do overestimate more than adults, it would be incorrect to omit the data from the 37-42°C range. Naturally, although the values of fl used here allow a comparison among ages (e.g. Fig. 3), they are not good
88
ROBERTO REFINETTI
Table 2. Literature data on magnitude estimation of warmth in adults Authors Figure cm2 s /~ rL rN
Graham C. H. (1950) Behavior, perception and the psychophysical methods. Psychol. Rev. 57, 108-120. Gray L., Stevens J. C. and Marks L. E. (1982) Thermal stimulus thresholds: sources of variability. Physiol. Behav. Stevens and Marks (1971) 2 4 3 0.44 0.92 0.99 29, 355-360. Herget et al. (1941) 4 15 2 0.61 0.97 0.98 Stevens et al. (1974) 5 200 3 0.65 1.00 0.99* Hensel H. (1981) Thermoreception and Temperature Regulation. Academic Press, London. Marks et al. (1976) 3 I1 2 0.68 0.99 1.00 Herget C. M., Granath L. P. and Hardy J. D. (1941). Stevens et al. (1974) 9 22 3 0.78 0.98 0.99 Thermal sensation and discrimination in relation to inMolinari et al. (1977) 4 7 12 0.93 1.00 1.00 Stevens and Marks (1971) 7 127 3 0.95 1.00 1.00 tensity of stimulus. Am. J. Physiol. 134, 6454555. Marks and Stevens (1973a) 1 22 1/2 1.02 0.98 0.99 Kenshalo D. R. and Scott H. A. Jr (1966) Temporal course Stevens et al. (1974) 5 10 3 1.04 1.00 1.00 of thermal adaptation. Science 151, 1095 1096. Marks and Stevens (1973b) 7 22 6 1.06 1.00 0.99* Marks L. E. and Stevens J. C. (1973a) Spatial summation Marks and Stevens (1973a) 4 l0 3 1.07 1.00 1.00 of warmth. Influence of duration and configuration of the Stevens and Stevens (1960) 2 7 3 1.59 0.99 0.96* stimulus. Am. J. Psychol. 86, 251-267. The data wereobtained from the figuresindicatedfor each paper and Marks L. E. and Stevens J. C. (1973b) Temporal summation interpolated by the least-squares method. Stimulus size (cm2) related to the nature of the proximal stimulus for the and duration (s), power-function exponent (fl), and linearwarmth sense. Percept. Psychophys. 14, 570-576. correlation coefficientsfor log-log data (rL) and natural data (rN) are shown. All correlation coefficientsare significantat the Marks L. E., Stevens J. C. and Tepper S. J. (1976) Interaction of spatial and temporal summation in the warmth 0.01 level or better. Asterisksshow the cases where rNis smaller sense. Sensor)' Processes 1, 87 98. then r L. Molinari H. H., Greenspan J. D. and Kenshalo D. R. (1977) The effects of rate of temperature change and adapting indices for calculating perceptual magnitude from temperature on thermal sensitivity. Sensory Processes I, stimulus magnitude. It should be noticed, in this 354-362. connection, that the exact value o f fl for w a r m t h Piaget J. (1969) The Mechanisms o f Perception (translated estimation remains controversial even in adults. As by Seagrim N. G.). Basic Books, New York. can be seen in Table 2, previous studies in adults have Siegel A. W. and McBurney D. H. (1970) Estimation of line found exponents from 0.44 to 1.59. A l t h o u g h the length and number: a developmental study. J. exp. Child Psychol. 10, 170-180. value o f fl is related to stimulus size (Stevens and Marks, 1971) and d u r a t i o n (Marks and Stevens, Sinclair D. (1981) Mechanisms o f Cutaneous Sensation. Oxford University Press, Oxford. 1973b) within individual studies, the different exp o n e n t s s h o w n in Table 2 are clearly not related to Stevens J. C. (1983) Thermal sensation: infrared and microwaves. In Microwaves and Thermoregulation (Edited by these two parameters. There is no a p p a r e n t explaAdair E. R.), pp. 191 201. Academic Press, New York. nation for the large variability in the results o b t a i n e d Stevens J. C. and Stevens S. S. (1960) Warmth and cold: in different studies. Practice tends to m o v e fl to 1.0, dynamics of sensory intensity. J. exp. Psychol. 60, larger values being reduced and smaller values being 183-192. increased (unpublished observations), but all subjects Stevens J. C. and Marks L. E. (1971) Spatial summation and the dynamics of warmth sensation. Percept. P~ychophys. in the studies cited above had extensive training 9, 391 398. before the experimental sessions. A curious detail in Table 2 is that in only 3 out o f Stevens J. C., Marks L. E. and Simonson D. C. (1974) Regional sensitivity and spatial summation in the warmth 12 cases is r N smaller than r L. This means that in m o s t sense. Physiol. Behav. 13, 825-836. cases the relationship between perceptual intensity Stevens S. S. (1970) Neural events and the psychophysical and stimulus magnitude is n o t better represented by law. Science 170, 1043-1050. a power function than by a linear function. In the Teghtsoonian M. (1980) Children's scales of length and present study, only 10 out o f 32 data sets were loudness: a developmental application of cross-modal represented better by a power function t h a n by a matching. J. exp. Child Psychol. 30, 290 -~307. Woolsey T. A., Durham D., Harris R. M., Simons D. J. and linear function. Valentino K. L. (1981) Somatosensory development. In REFERENCES Development o f Perception (Edited by Aslin R. N., Alberts J. R. and Petersen M. R.), Vol. 1, pp. 259--292. Academic Briick K. (1978) Heat production and temperature reguPress, New York. lation. In Perinatal Physiology (Edited by Stave U.), pp. 455~,98. Plenum Medical, New York.