Abstract
An Operational Momentum (OM) effect is shown by 9-month-old infants during non-symbolic arithmetic, whereby they overestimate the outcomes to addition problems, and underestimate the outcomes to subtraction problems. Recent evidence has shown that this effect extends to ordering operations for size-based sequences in 12-month-olds. Here we provide evidence that OM occurs for ordering operations involving numerical sequences containing multiple quantity cues, but not size-based sequences, already at 4 months of age. Infants were tested in an ordinal task in which they detected and represented increasing or decreasing variations in physical and/or numerical size, and then responded to ordinal sequences that exhibited greater or lesser sizes/numerosities, thus following or violating the OM generated during habituation. Results showed that OM was absent during size ordering (Experiment 1), but was present when infants ordered arrays of discrete elements varying on numerical and non-numerical dimensions, if both number and continuous magnitudes were available cues to discriminate between with-OM and against-OM sequences during test trials (Experiments 2 vs. 3). The presence of momentum for ordering number only when provided with multiple cues of magnitude changes suggests that OM is a complex phenomenon that blends multiple representations of magnitude early in infancy.
Highlights
An Operational Momentum (OM) effect is shown by 9-month-old infants during non-symbolic arithmetic, whereby they overestimate the outcomes to addition problems, and underestimate the outcomes to subtraction problems
Binomial tests confirmed the absence of an OM effect in this experiment, revealing that 22 out of 40 infants looked longer to the against-OM test trial compared to the with-OM one (22 vs. 18, p = .6; two-tailed), with a similar number of infants showing the pattern in the increasing and decreasing conditions (9 vs. 13, n.s.)
This study investigated whether OM effects recently described for ordinal operations in size-based sequences by 12-month-old infants (Macchi Cassia et al, 2016) are present in 4-month-old infants, who are already able to represent ordinal information for the dimensions of size (Macchi Cassia et al, 2012) and number
Summary
An Operational Momentum (OM) effect is shown by 9-month-old infants during non-symbolic arithmetic, whereby they overestimate the outcomes to addition problems, and underestimate the outcomes to subtraction problems. It is widely accepted that numerical representations take the form of a ‘mental number line’ This model posits that numerosities are spatially represented along a continuum, such that (in Western cultures) small numbers are associated to the left side and large numbers to the right side of space, first evidenced by the so-called SNARC (Spatial-Numerical Association of Response Codes) effect (Dehaene, Bossini, & Giraux, 1993). Bulf and colleagues (Bulf et al, 2016) found that 8-month-old infants orient faster towards a left-sided cue when previously primed by a central small numerosity, and they orient faster to a right-sided cue when previously primed by a central large numerosity This evidence suggests that numerical representations have an inherent spatial component, which points to the existence of a spatially oriented numerical representation that is functional in the first year of life
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