ScienceWeek

MEDICAL BIOLOGY: SEX DIFFERENCES IN READING DISABILITY

The following points are made by M. Rutter et al (J. Am. Med. Assoc. 2004 291:2007):

1) Are boys more likely than girls to have reading disability? The answer to this question has both theoretical implications (with respect to possible causal mechanisms) and practical implications (with respect to service provision). If boys are truly more likely to have reading disability, this would direct research attention to uncovering the possible source of the sex difference. Also, the sex difference would offer a window into the understanding of the causal processes involved in the origins of developmental reading disability.(1) In addition, if boys are more prone to have reading disability, this should motivate educational programs to address boys' early emerging disability. Given that reading disability in childhood is associated with adjustment problems and long-term adverse outcomes in multiple life domains,(2) the elucidation of this disability should constitute a high priority.

2) Thirty years ago, epidemiological studies drew attention to the preponderance of male children with reading disability. Surveys both on the Isle of Wight and in an inner London borough(3) were consistent in showing that reading disability, whether assessed through group or individual tests, was substantially more frequent in boys than in girls. Moreover, the sex difference was evident whether reading disability was considered in terms of IQ-referenced (adjusted) specific reading retardation (in which reading was markedly lower than that predicted on the basis of age and IQ) or non-IQ-referenced general low achievement in reading. Thus, in the inner London sample of 10-year-olds, the rates of specific reading retardation on group tests were 16.9% in boys compared with 7.2% in girls. Using individual testing in those with positive screens on the group reading test, the rates were 4.6% vs 2.0%. The comparable data for Isle of Wight 10-year-old boys and girls were 8.6% vs 3.7% on group tests and 5.6% vs 2.9% on individual tests.3

3) When non-IQ-referenced reading disability was defined as performance at least 28 months behind population norms on either reading accuracy or reading comprehension, the male-female difference on group tests was 15.9% vs 7.2% in inner London, with 22.2% vs 15.6% on the basis of individual testing of those who had positive screens. The comparable Isle of Wight data were 8.6% vs 3.7% on group testing and 10.5% vs 6.1% on individual testing. The sample sizes in both cases were large: 1689 for the inner London 10-year-olds and 1142 for the Isle of Wight 10-year-olds.

4) Some 15 years later, in 1990, Shaywitz et al,(4) reporting on a sample of 414 children aged 7 to 8 years, drew attention to their finding that the sex ratio in their epidemiological study was very much less than that in their sample of children identified on the basis of school records. Among the children in second grade, the rates were 8.7% in boys vs 6.9% in girls, and 1 year later (at a mean age of 8.7 years), the comparison was 9.0% vs 6.0%.

5) The authors summarize the history of research on sex differences in reading disability and provide new evidence from four independent epidemiological studies about the nature, extent, and significance of sex differences in reading disability. In all 4 studies, the rates of reading disability were significantly higher in boys. The authors conclude: "Reading disabilities are clearly more frequent in boys than in girls."(5)

References (abridged):

1. Rutter M, Caspi A, Moffitt TE. Using sex differences in psychopathology to study causal mechanisms: unifying issues and research strategies. J Child Psychol Psychiatry. 2003;44:1092-1115

2. Snowling MJ. Reading and other learning difficulties. In: Rutter M, Taylor E, eds. Child and Adolescent Psychiatry, 4th Edition. Oxford, England: Blackwell Science; 2002:682-696

3. Berger M, Yule W, Rutter M. Attainment and adjustment in two geographical areas, II: the prevalence of specific reading retardation. Br J Psychiatry. 1975;126:510-519

4. Shaywitz SE, Shaywitz BA, Fletcher JM, Escobar MD. Prevalence of reading disability in boys and girls: results of the Connecticut Longitudinal Study. JAMA. 1990;264:998-1002

5. Flannery KA, Liederman J, Daly L, Schultz J. Male prevalence for reading disability is found in a large sample of black and white children free from ascertainment bias. J Int Neuropsychol Soc. 2000;6:433-442

J. Am. Med. Assoc. http://www.jama.com

--------------------------------

Related Material:

SEX DIFFERENCES IN THE NEURAL BASIS OF EMOTIONAL MEMORIES.

The following points are made by T. Canli et al (Proc. Nat. Acad. Sci. 2002 99:11802):

1) Emotionally arousing experiences are more memorable than neutral experiences. There is superior memory for traumatic relative to mundane events (1) and for emotionally provocative relative to neutral words (2) and pictures (3). Memory for emotional stimuli and experiences differs between the sexes (4,5). Women recall more emotional autobiographical events than men in timed tests, produce memories more quickly or with greater emotional intensity in response to cues, and report more vivid memories than their spouses for events related to their first date, last vacation, and a recent argument (4).

2) Two explanations for the difference in memory performance have been proposed. The "affect-intensity" hypothesis posits that women have better memory because they experience life events more intensely than men and thus may better encode such events into memory (4). Controlling for affect intensity at encoding should therefore eliminate women's superior memory performance. The "cognitive-style" hypothesis posits that women may differ from men in how they encode, rehearse, or think about their affective experiences or in how they generate responses in a memory test (5). According to this view, controlling for affect intensity at encoding should not remove sex-based differences in memory performance.

3) In summary: Psychological studies have found better memory in women than men for emotional events, but the neural basis for this difference is unknown. The authors report they used event-related functional MRI to assess whether sex differences in memory for emotional stimuli is associated with activation of different neural systems in men and women. Brain activation in 12 men and 12 women was recorded while they rated their experience of emotional arousal in response to neutral and emotionally negative pictures. In a recognition memory test 3 weeks after scanning, highly emotional pictures were remembered best, and remembered better by women than by men. Men and women activated different neural circuits to encode stimuli effectively into memory even when the analysis was restricted to pictures rated equally arousing by both groups. Men activated significantly more structures than women in a network that included the right amygdala, whereas women activated significantly fewer structures in a network that included the left amygdala. Women had significantly more brain regions where activation correlated with both ongoing evaluation of emotional experience and with subsequent memory for the most emotionally arousing pictures. Greater overlap in brain regions sensitive to current emotion and contributing to subsequent memory may be a neural mechanism for emotions to enhance memory more powerfully in women than in men.

References (abridged):

1. Christianson, S.-A. & Loftus, E. F. (1987) Appl. Cogn. Psychol. 1, 225-239.

2. LaBar, K. S. & Phelps, E. A. (1998) Psychol. Sci. 9, 490-493.

3. Bradley, M. M. , Greenwald, M. K. , Petry, M. C. & Lang, P. J. (1992) J. Exp. Psychol. Learn. Mem. Cognit. 18, 379-390.

4. Fujita, F. , Diener, E. & Sandvik, E. (1991) J. Pers. Soc. Pychol. 61, 427-434.

5. Seidlitz, L. & Diener, E. (1998) J. Pers. Soc. Pychol. 74, 262-271.

Proc. Nat. Acad. Sci. http://www.pnas.org

--------------------------------

Related Material:

COGNITIVE SCIENCE: SEX DIFFERENCES IN CHIMPANZEE LEARNING

The following points are made by E.V. Lonsdorf et al (Nature 2004 428:715):

1) The wild chimpanzees in Gombe National Park, Tanzania, fish for termites with flexible tools that they make out of vegetation, inserting them into the termite mound and then extracting and eating the termites that cling to the tool(1). Tools may be used in different ways by different chimpanzee communities according to the local chimpanzee culture(2).

2) Chimpanzees use tools for more purposes than any other non-human species(3). The cultural variation in tool-use repertoires among chimpanzee communities may be attributable to individuals socially learning from other members of their community(2). The authors investigated this process in wild chimpanzees in Gombe National Park by videotaping 14 animals (who were all under 11 years old) and their mothers during termite-fishing sessions.

3) There were no significant differences between the sexes in the frequency of social interaction with the mothers, and mothers did not show any difference in tolerance towards male or female offspring. Because active demonstration of nut-cracking by a chimpanzee mother in the Tai forest has been described(5), the authors looked for evidence of such behavior in mothers at Gombe. They saw no cases of active teaching, by mothers or any other individuals, which would have been indicated, for example, by the offering of tools or modification of offspring behavior.

4) The authors conclude: "Our findings indicate that female chimpanzees start to fish for termites at a younger age than males; they are more proficient than males once they have acquired the skill; and they each use a technique similar to their mother's, although males do not. To our knowledge, this is the first systematic evidence of a difference between the sexes in the learning or imitation of a tool-use technique in wild chimpanzees. A similar disparity in the ability of young males and females to learn skills has been demonstrated in human children and may be indicative of different learning processes. A sex-based learning difference may therefore date back at least to the last common ancestor of chimpanzees and humans.(3,4)

References (abridged):

1. Goodall, J. Symp. Zool. Soc. Lond. 10, 39-48 (1963)

2. Whiten, A. et al. Nature 399, 682-685 (1999)

3. McGrew, W. C. Chimpanzee Material Culture: Implications for Human Evolution (Cambridge Univ. Press, Cambridge, 1992)

4. McCulloch, C. E. & Searle, S. R. Generalized, Linear, and Mixed Models (Wiley, New York, 2000)

5. Boesch, C. Anim. Behav. 41, 530-532 (1991)

Nature http://www.nature.com/nature

ScienceWeek http://scienceweek.com