Using psychophysical tools to quantify body image perception: a tutorial

Mauerberg-deCastro, Eliane; Tavares, Carolina Paioli; Paula, Adriana Inês de; Crozara, Gabriella Braga; Campbell, Debra Frances

doi:10.1590/S1980-65742015000400001

Eliane Mauerberg-deCastro

Universidade Estadual Paulista, Rio Claro, SP, Brazil

Carolina Paioli Tavares

Universidade Estadual de Ponta Grossa, Ponta Grossa, PR, Brazil

Adriana Inês de Paula

Universidade Estadual de Ponta Grossa, Ponta Grossa, PR, Brazil

Gabriella Braga Crozara

Academia da Força Aérea Brasileira, Pirassununga, SP, Brazil

Debra Frances Campbell

Universidade Estadual Paulista, Rio Claro, SP, Brazil

Eliane Mauerberg-deCastro, Sc.D. LAP, DEF, UNESP Av. 24-A, 1515, Bela Vista, Rio Claro 13506-900 SP, Brazil E-mail: mauerber@rc.unesp.br

Authors' note Eliane Mauerberg-deCastro (Sc.D., Psychobiology) and Debra Frances Campbell (Ph.D., Technology and Human Development) are affiliated with the Laboratory of Action and Perception, São Paulo State University (Universidade Estadual Paulista), Rio Claro, SP, Brazil. Carolina Paioli Tavares (Ph.D., Movement Sciences) and Adriana Inês de Paula (Ph.D., Movement Sciences) are affiliated with the State University of Ponta Grossa (Universidade Estadual de Ponta Grossa), Ponta Grossa, PR, Brazil. Gabriella Braga Crozara (M.S., Movement Sciences) is affiliated with the Brazilian Air Force Academy (Academia da Força Aérea Brasileira), Pirassununga, SP, Brazil.

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Figure 1
Scale of distorted images of a female participant's body, including the actual, undistorted image (i.e., 100% or BMI = 23.3).

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Figure 2
Pair of two images of a participant's body, undistorted (100% or BMI = 26.7, top) and distorted (200% or BMI = 40, bottom).

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Figure 3
Magnitude estimation of perceived size of distorted body images (psychological scale) and the actual size of distorted body images (physical scale) representing the CE (BMI_dif) of a female individual.

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Figure 4
Di-log plots of perceived size of body in images (psychological scale) and the actual size of distorted body images (physical scale), using logarithmic values for estimations of magnitude of two different individuals. The first shows a perceptual constancy ( left side ) and the second, a perceptual overconstancy ( right side ).

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Figure 5
Geometric mean of the power function's exponents in two psychophysical magnitude estimation tasks, with distorted body images of own body and a stranger's body of a group of female adolescents at risk for body image disorders ( Paula, 2010Paula, A.I. (2010). Percepção de dimensões corporais de adolescentes do sexo feminino. Aspectos psicofísicos e comportamentais (Perception of body size of female adolescents. Psychophysical and behavioral aspects). 82 f. Tese (Doutorado em Ciências da Motricidade), Departamento de Educação Física, Universidade Estadual Paulista (UNESP), Rio Claro.). (Standard errors in bars.)

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Figure 6
Two examples of pairs of images that are distorted on one side only (on right is the actual, undistorted image; on left is the distorted image). Male participant is from the control group ( Braga, 2012Braga, G.F. (2012). Percepção da imagem corporal de adultos após acidente vascular encefálico: uma abordagem psicofísica (Body image perception after stroke adults: a psycho-physical approach). 94 f. Dissertação (Mestrado em Ciências da Motricidade), Departamento de Educação Física, Universidade Estadual Paulista (UNESP), Rio Claro.).

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Figure 7
Geometric mean of the power function's exponents of two groups of male participants (sports and fitness) for magnitude estimation of own body image and strangers', and own body image without face ( Tavares, 2015Tavares, C.P. (2015). Aspectos psicofísicos da imagem corporal e a sua relação com a dismorfia muscular e a dependência de exercício (Psychophysical aspects of body image and their relationship with muscle dysmorphia and exercise dependence). 122 f. Tese (Doutorado em Ciências da Motricidade), Departamento de Educação Física, Universidade Estadual Paulista (UNESP), Rio Claro.).

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Since the late 18th Century, scientists have used psychophysics to measure perceptual and sensory systems. Simply defined, psychophysics is, "The branch of psychology concerned with the effects of physical stimuli on mental processes" ( DaSilva & Ribeiro-Filho, 2006). However, psychophysics is both an area of study and a methodology. The investigation of human perception is centered on human experiences-at different levels of development or adaptation-of space, objects, and events, and of their dimensions. Wundt, in 1879, founded the first laboratory of experimental psychology in which studies about consciousness and perception included introspective methods ( Stevens, 1951; 1975). Introspective methods in the field of perception and psychophysics were abandoned because of the lack of validity, reliability, and new developments in the field, with the advancement of technology and the appearance of animal psychology. For almost two centuries, scientists of human behavior-mostly psychologists-were intrigued with the possibility of measuring, predicting, and eventually explaining how humans perceive the world. The reliability of early investigations conflicted with the subjectivism of introspective techniques. Given the vast range of possibilities an individual has to express himself, in an experimental situation his impressions of a given stimulus lent little reliability to introspective methods (i.e., analytical insight). These methods left it open to the individual to describe (typically verbal replies) what he perceived about a stimulus. Studies on sensation and perception since psychometrics' early history have resulted in numerous applications, including: • Information theory (marketing, advertising, education, internet applications, intelligence) • Development of communication technology and radar systems (military use) • Space programs (humans outside of the terrestrial environment and effects of microgravity) • Artificial intelligence (human-machine analogies, computers, robots) • Ergonomics (implementation of service equipment in daily life activities, sport, work, leisure) • Rehabilitation (prostheses, implants, stimulation techniques, adaptations after intervention) • Public health (consumerism, hygiene habits, disease prevention, lifestyle choices) • Architecture and urban design (spaces and utilities, comfort and aesthetics, technological growth and demand) • Social behavior (mass behavior, perception of face and body image, public safety, institutional behavior, traffic, war)

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Table 1
Example of the calculation of a geometric progression of a limited scale of image sizes for a participant (BMI = 23.3).

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Table 2
Example of the calculation of two sub-scales of a geometric progression of a limited scale of image sizes for a participant (BMI = 26.6).

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Table 3
Outcome of the calculation of the two sub-scales of a geometric progression of a limited scale of image sizes for a participant with a BMI of 26.6.

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Table 4
Participants' responses (% and BMI) to seven distorted images, and outcomes, respectively, for %_dif and BMI_dif.

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Table 5
Example of an experimental trial with seven distorted images with respective values, S (%), and a participant's magnitude estimation response, R (%). Each magnitude set (S and R) was converted into log, x_i (log Si ), and y_i (log R_i ).

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Table 6
Exponent of the psychophysical power function and the coefficient of determination of participants in two groups: Young adults and stroke survivors performed an estimation of magnitude task in which their own body images were bisected.

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Since the late 18th Century, scientists have used psychophysics to measure perceptual and sensory systems. Simply defined, psychophysics is, "The branch of psychology concerned with the effects of physical stimuli on mental processes" ( DaSilva & Ribeiro-Filho, 2006Da Silva, J.A., & Ribeiro-Filho, N.P. (2006). Avaliação e mensuração de dor: pesquisa, teoria e prática (Assessment and measurement of pain: research, theory and practice). Ribeirão Preto: Funpec, 467p.). However, psychophysics is both an area of study and a methodology. The investigation of human perception is centered on human experiences-at different levels of development or adaptation-of space, objects, and events, and of their dimensions. Wundt, in 1879, founded the first laboratory of experimental psychology in which studies about consciousness and perception included introspective methods ( Stevens, 1951Stevens, S.S. (Ed.) (1951). Handbook of Experimental Psychology. New York: Wiley.; 1975Stevens, S.S. (1975). Psychophysics: introduction to its perceptual, neural and social prospects. New York: Wiley.). Introspective methods in the field of perception and psychophysics were abandoned because of the lack of validity, reliability, and new developments in the field, with the advancement of technology and the appearance of animal psychology. For almost two centuries, scientists of human behavior-mostly psychologists-were intrigued with the possibility of measuring, predicting, and eventually explaining how humans perceive the world. The reliability of early investigations conflicted with the subjectivism of introspective techniques. Given the vast range of possibilities an individual has to express himself, in an experimental situation his impressions of a given stimulus lent little reliability to introspective methods (i.e., analytical insight). These methods left it open to the individual to describe (typically verbal replies) what he perceived about a stimulus. Studies on sensation and perception since psychometrics' early history have resulted in numerous applications, including: • Information theory (marketing, advertising, education, internet applications, intelligence) • Development of communication technology and radar systems (military use) • Space programs (humans outside of the terrestrial environment and effects of microgravity) • Artificial intelligence (human-machine analogies, computers, robots) • Ergonomics (implementation of service equipment in daily life activities, sport, work, leisure) • Rehabilitation (prostheses, implants, stimulation techniques, adaptations after intervention) • Public health (consumerism, hygiene habits, disease prevention, lifestyle choices) • Architecture and urban design (spaces and utilities, comfort and aesthetics, technological growth and demand) • Social behavior (mass behavior, perception of face and body image, public safety, institutional behavior, traffic, war)

BMI limit for thinness		BMI limit for heaviness/obesity
BMI: 16 ( S_i, or initial stimulus)		BMI: 40 ( S_t, or terminal stimulus)
S_i = 16 ∙ 100/23.3		S_t = 40 ∙ 100/23.3
S_i= ~68.7 (%)		S_t = ~171.7 (%)
	S_t = S_i + ( n − 1) r
	171.7 = 68.7 + (10 − 1) r
	9 r = 103
	r = 11.4

BMI limit for thinness	BMI limit for heaviness/obesity
BMI: 16 ( S_i, or stimulus)	BMI: 40 ( S_f, or stimulus)
S_i = 16 ∙ 100/26.6	S_f = 40 ∙ 100/26.6
Si = ~60.1 (%)	S_f= ~150.4 (%)
S_{t lower} = S_i + ( n -1) r	S_{t upper} = S_i + ( n − 1) r
100 = 60.1 + (4-1) r	150.4 = 100 + (4 − 1) r
3 r = 39.9	3 r = 50.4
r_lower = 13.3	r_upper = 16.8

Calculating the stimulus increment using r	Percentage (%)	BMI value
S ₁	60.1	16
S₁ + r_lower = S₂	73.4	19.5
S₂ + r_lower = S₃	86.7	23.1
S ₄	100	26.6
S₄ + r_upper = S₅	116.8	31.1
S₅ + r_upper = S₆	133.6	35.5
S ₇	150.4	40

Stimulus (S) (%)	Stimulus (S) (BMI)	Response (R) (%)	Response (R) (BMI)	%dif	BMIdif
69.3	16.5	55	13.1	-14.3	-3.4
80.3	19.1	65	15.5	-15.3	-3.6
93.1	22.1	80	19.0	-13.1	-3.1
107.9	25.7	120	28.6	12.1	2.9
123.0	29.7	150	35.7	25.0	5.9
144.8	34.5	170	40.5	25.2	6.0
167.8	39.9	250	59.5	82.2	19.5
Absolute error (AE)		26.7	6.3

Young adults (N = 17)
	Whole body	Right-side distortion	Left-side distortion
n	1.2	1.4	1.4
r ²	.91	.93	.93
Stroke survivors ( N = 15)			.93
	Whole body ( N = 11)	Right-side distortion ( N = 9)	Left-side distortion ( N = 7)
n	1.2	0.90	0.88
r ²	.83	.78	.77

Young adults (N = 17)
	Whole body	Right-side distortion	Left-side distortion
n	1.2	1.4	1.4
r ²	.91	.93	.93
Stroke survivors ( N = 15)			.93
	Whole body	Right-side distortion	Left-side distortion
	( N = 11)	( N = 9)	( N = 7)
n	1.2	0.90	0.88
r ²	.83	.78	.77

[1] Eliane Mauerberg-deCastro, Sc.D. LAP, DEF, UNESP Av. 24-A, 1515, Bela Vista, Rio Claro 13506-900 SP, Brazil E-mail: mauerber@rc.unesp.br

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