Abstract
To test whether atypical number development may affect other types of quantity processing, we investigated temporal discrimination in adults with developmental dyscalculia (DD). This also allowed us to test whether number and time may be sub-served by a common quantity system or decision mechanisms: if they do, both should be impaired in dyscalculia, but if number and time are distinct they should dissociate. Participants judged which of two successively presented horizontal lines was longer in duration, the first line being preceded by either a small or a large number prime (“1” or “9”) or by a neutral symbol (“#”), or in a third task participants decided which of two Arabic numbers (either “1,” “5,” “9”) lasted longer. Results showed that (i) DD’s temporal discriminability was normal as long as numbers were not part of the experimental design, even as task-irrelevant stimuli; however (ii) task-irrelevant numbers dramatically disrupted DD’s temporal discriminability the more their salience increased, though the actual magnitude of the numbers had no effect; in contrast (iii) controls’ time perception was robust to the presence of numbers but modulated by numerical quantity: therefore small number primes or numerical stimuli seemed to make durations appear shorter than veridical, but longer for larger numerical prime or numerical stimuli. This study is the first to show spared temporal discrimination – a dimension of continuous quantity – in a population with a congenital number impairment. Our data reinforce the idea of a partially shared quantity system across numerical and temporal dimensions, which supports both dissociations and interactions among dimensions; however, they suggest that impaired number in DD is unlikely to originate from systems initially dedicated to continuous quantity processing like time.
Highlights
Developmental dyscalculia (DD) is a congenital and specific learning disability affecting the understanding of numerical concepts and arithmetical information in the context of normal intelligence (American Psychiatric Association, 1994), and affecting 4–7% of the population (Shalev et al, 2005; Shalev, 2007)
It is unclear whether these self-reports reflect a genuine disability in time perception and cognition, or whether they are more related to a difficulty in performing numerical operations relating to time, for instance in calculating how much time is needed to get to an appointment
There were three principle findings: (i) in contrast to their numerical impairment, DD’s temporal discrimination showed comparable acuity to controls, with reliable discrimination between two lines differing in duration; (ii) in DD discrimination became abnormally poor when the identical line stimuli were preceded by numerical primes, even though these were task-irrelevant, or when durations were judged on numerical stimuli directly; (iii) there were distinct interactions between time and numbers for controls vs DDs: for controls, but not DD, the perception of duration appeared to be modulated by the value of task-irrelevant numbers
Summary
Developmental dyscalculia (DD) is a congenital and specific learning disability affecting the understanding of numerical concepts and arithmetical information in the context of normal intelligence (American Psychiatric Association, 1994), and affecting 4–7% of the population (Shalev et al, 2005; Shalev, 2007). Most research on DD has focused on the ability to process numbers represented symbolically or non-symbolically and on arithmetical skills (e.g., Butterworth et al, 2011) To date, it is still unknown whether dyscalculia affects solely number quantity processing or whether it extends to other non-numerical quantity dimensions such as luminance, physical size, or time. DD subjects frequently report poor ability to appreciate time which is often exemplified by their unreliable punctuality at appointments or by their inability to plan activities It is unclear whether these self-reports reflect a genuine disability in time perception and cognition, or whether they are more related to a difficulty in performing numerical operations relating to time, for instance in calculating how much time is needed to get to an appointment. We aimed to test whether congenitally malfunctioning number processing may extend to time processing
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