Development of magnitude processing in children with developmental dyscalculia: space, time, and number.

Kenny Skagerlund,Ulf Trã¤Ff

doi:10.3389/fpsyg.2014.00675

Abstract

Developmental dyscalculia (DD) is a learning disorder associated with impairments in a preverbal non-symbolic approximate number system (ANS) pertaining to areas in and around the intraparietal sulcus (IPS). The current study sought to enhance our understanding of the developmental trajectory of the ANS and symbolic number processing skills, thereby getting insight into whether a deficit in the ANS precedes or is preceded by impaired symbolic and exact number processing. Recent work has also suggested that humans are endowed with a shared magnitude system (beyond the number domain) in the brain. We therefore investigated whether children with DD demonstrated a general magnitude deficit, stemming from the proposed magnitude system, rather than a specific one limited to numerical quantity. Fourth graders with DD were compared to age-matched controls and a group of ability-matched second graders, on a range of magnitude processing tasks pertaining to space, time, and number. Children with DD displayed difficulties across all magnitude dimensions compared to age-matched peers and showed impaired ANS acuity compared to the younger, ability-matched control group, while exhibiting intact symbolic number processing. We conclude that (1) children with DD suffer from a general magnitude-processing deficit, (2) a shared magnitude system likely exists, and (3) a symbolic number-processing deficit in DD tends to be preceded by an ANS deficit.

Highlights

During the past 10 years, researchers have paid increasing attention to the origin and etiology of developmental dyscalculia (DD; prevalence rate = 3.5–7%; Shalev, 2007; Rubinsten and Henik, 2009)
The participants were divided into three groups: children with DD enrolled in their 4th year, a control group consisting of children with mathematical ability typical of 4th year students in the Swedish educational system (TA4), and an ability-matched control group of typical second graders (TA2)
While a deficit in the innate and preverbal approximate number system (ANS) previously had been suggested to play a role, our results support the notion that impaired ANS acuity in children with DD is the cause, rather than the effect, of impaired exact symbolic number processing

Summary

Introduction

Evidence is mounting that DD should be characterized as a weakness or deficit in innate number sense or numerosity coding (Butterworth, 2005; Wilson and Dehaene, 2007), where both terms refer to a cognitive component responsible for the apprehension and manipulation of numerosities. The numerosity-coding hypothesis states that DD is caused by a deficit in the processing of smaller and exact sets of numbers (Butterworth, 2010). This preverbal ability to represent and manipulate quantities may constitute the foundation for the symbolic number system used for learning formal arithmetic (e.g., Dehaene, 2011). As young children develop language and a language-based symbolic number system (i.e., counting words and digits), it is believed there is a mapping of the counting words and visual symbols onto the innate number system (Starkey and Cooper, 1980; Gallistel and Gelman, 1992; Wynn, 1992, 1995; Xu and Spelke, 2000; Feigenson et al, 2004; Gelman and Butterworth, 2005; Piazza, 2010; Dehaene, 2011)

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