Electrophysiological evidence for internalized representations of canonical finger-number gestures and their facilitating effects on adults' math verification performance

Abstract

Fingers facilitate number learning and arithmetic processing in early childhood. The current study investigated whether images of early-learned, culturally-typical (canonical), finger montring patterns presenting smaller (2,3,4) or larger (7,8,9) quantities still facilitate adults' performance and neural processing in a math verification task. Twenty-eight adults verified solutions to simple addition problems that were shown in the form of canonical or non-canonical finger-number montring patterns while measuring Event Related Potentials (ERPs). Results showed more accurate and faster sum verification when sum solutions were shown by canonical (versus non-canonical) finger patterns. Canonical finger montring patterns 2-4 led to faster responses independent of whether they presented correct or incorrect sum solutions and elicited an enhanced early right-parietal P2p response, whereas canonical configurations 7-9 only facilitated performance in correct sum solution trials without evoking P2p effects. The later central-parietal P3 was enhanced to all canonical finger patterns irrespective of numerical range. These combined results provide behavioral and brain evidence for canonical cardinal finger patterns still having facilitating effects on adults' number processing. They further suggest that finger montring configurations of numbers 2-4 have stronger internalized associations with other magnitude representations, possibly established through their mediating role in the developmental phase in which children acquire the numerical meaning of the first four number symbols.

Figure 1

Canonicity effects on reaction time for the low and high numerical ranges and for incorrect and correct sum solution trials (three-way Canonicity × Numerical Range × Solution interaction).

Figure 2

Grand average ERP’s at the left parietal (P3) electrode (left panel) and the right parietal (P4) electrode (right panel) with the P2p time window used in the analysis indicated by the grey bar. Topography plots for the 220–310 ms (P2p) time-window are shown separately for correct (top panel) and incorrect (bottom panel) sum solution trials in the four Canonicity-Range categories: Canonical-Low, Non-Canonical-Low, Canonical-High, Non-Canonical-High. The ERP plots show the grand average ERPs and topo-plots in all conditions of the experiment for purposes of evaluation of ERP quality and choice of windows and electrodes for analyses (see: Keil et al.). For visualization of the specific interaction effects found on P2p and P3 amplitude we refer the reader to Fig. 4A. Images are created by the first author using ERPlab software.

Figure 3

Grand average ERP’s (averaged over CPz and Cz electrodes) with the P3 time window indicated by the grey bar; left and right ERP graphs respectively show the grand average ERPs on correct and incorrect sum solution trials. Topography plots for the 280–550 ms (P3) time-window for correct and incorrect sum solution trials in the four Canonicity-Range categories: Canonical-Low, Non-Canonical-Low, Canonical-High, Non-Canonical-High. The ERP plots show the grand average ERPs and topo-plots in all conditions of the experiment for purposes of evaluation of ERP quality and choice of windows and electrodes for analyses (see: Keil et al.). For visualization of the specific interaction effects found on P2p and P3 amplitude we refer the reader to Fig. 4B. Images were created by the first author using ERPlab software.

Figure 4

Top: Mean P2p amplitude (averaged across the 220–310 ms time window) at left and right hemisphere parietal (P3 and P4) electrodes in the four Canonicity-Range conditions: Canonical-Low, Non-Canonical-Low, Canonical-High, Non-Canonical-High. The figure shows the three-way interaction between Canonicity, Range and Hemisphere with a statistically significant canonicity effect on P2p amplitude occurring only in response to finger-number configurations showing small numerosities 2–4 above the right parietal hemisphere. Bottom: Mean P3 amplitude averaged across CPz and Cz electrodes in the four Solution-Range categories: Incorrect-Low, Correct-Low, Incorrect-High, Correct-High, showing the Solution × Range interaction with a larger numerical range effect on P3 amplitude (enhanced activation in response to hands showing small numbers 2–4) on trials with correct compared to incorrect sum solutions.

Figure 5

The Math Task (top) showing two examples of addition problems presented in Arabic Numerals, followed by a variable interval (between 300 and 900 ms), followed by a problem solution presented by the hands (foreground: incorrect problem solution represented by a canonical finger configuration; background: correct problem solution represented by a non-canonical finger representation). The montring finger stimuli (bottom) were composed of canonical (top row) or non-canonical (bottom row) patterns combined with an open (top row left) or closed hand (bottom row left). Task stimuli were drawn hands obtained from the internet (see Ref.), but due to copyright considerations photos of the presented postures are shown in this figure.