An ERP Study On The Representation Of Two-Digit Number In Stroop Paradigm

Numeral representation mainly involving in number processing refers to the awareness and understanding of number, which remains the focus in mathematical cognition. In one-digit Arabic numerals processing, individuals transform specific magnitude or number to abstractly mental number line. Due to the different types of information recording, the processing mechanism of two-digit is different from that of one-digit number.The magnitude and physical size congruency effect and unit-decade compatible effect are the two important phenomena in Stroop experimental paradigm. The stimuli in numerical Stroop task have magnitude dimension and physical dimension, and two conditions of congruent and incongruent in magnitude size and physical size. The inconsistence of the two dimensions causes conflict effect, whereas the consistence of the two dimensions leads to facilitation effect. This effect is known as congruency effect of magnitude size and physical size. A pair of two-digit number divides into compatible and incompatible condition:a given number comparison is defined as unit-decade-compatible if both comparisons between tens and units led to the same decision (e.g., for 42₅7,both 4<5 and 2<7). In contrast, a number comparison is defined as unit-decade incompatible, if the two comparisons for units and tens lead to different decisions (e.g., for 47₆2; 4<6,but 7>2). Incompatible number pairs are responded to more slowly than compatible number pairs, which is called unit-decade compatible effect.ERP technology can record the EEG during two-digit number processing:P300 mainly reflects the recognition to the number attribute and degree of attention; N400 is the electric signal of information processing to semantic association; LRP is a measure of motor cortex activation, and it indicates selective motor preparation and response initiation before an overt response is given. Magnitude and physical size congruency effect and unit-decade compatible effect can be reflected in the changes of P300/N400/LRP latency and amplitude. It was hypothesized that the two-digit number involved both holistic and decomposed processing, manifesting in magnitude and physical size congruency effect and unit-decade compatible effect. Taken adult college students as participants, two ERP experiments were designed to verify these hypotheses.Experiment 1 employed physical size comparison task of two-digit Arabic number. Electrical Geodesics Incorporated system was used to record the response time, latency, et al. The statistics analysis showed that:in reaction time as well as the P300, LRP latency, amplitude, size congruency effect was significant, indicating a holistic processing of two-digit representation; in the P300, N400 and LRP latency and amplitude, unit-decade compatibility had significant effect, indicating that there was decomposed processing in two-digit number; the topography results showed that left and right hemisphere automatically processed the two-digit number in mutual cooperation.The luminance comparison task of two-digit number was used in Experiment 2. The results indicated:in the reaction time and P300,N400 latency, amplitude,the luminance congruency effect was significant, showing that the magnitude information of two-digit number had holistic processing; in the same response index, unit-decade compatible effect was significant, providing decomposed processing evidence; topography analysis suggested two-digit number processing needs two hemispheres together.Conclusively, the ERP research on the representation of two-digit number in Stroop paradigm confirms all the hypotheses. In automatic processing of number magnitude, the processing of two-digit number shows magnitude and physical size congruency effect and unit-decade compatible effect, which suggests that the two-digit number has holistic and decomposition representation. This study deepens the understanding of our understanding of double-digit processing, and reveals the mental representation mechanism of two-digit number. These findings enrich the theory of digital processing; and also help to guide education and research in school mathematics and develop mathematical thinking abilities.