| Dehaene and colleagues (1993) discovered an association of smaller numbers with the left motor responses, and larger numbers with the right motor responses, which they termed the SNARC effect. They attempted to explain the occurrence of this effect in terms of a mental number line representation. Recent evidence, however, has challenged the mental number line notion and thus the SNARC effect still stands short of a comprehensive explanation. Based on McNamara and colleagues' model of spatial cognition (Kelly, & McNamara, 2003; McNamara, Rump, & Werner, 2003; Mou, Fan, McNamara, & Owen, 2008; Mou, Li, & McNamara, 2008; Mou, & McNamara, 2002; Mou, McNamara, Valiquette, & Rump, 2004; Mou, Zhang, & McNamara, 2004; Shelton & McNamara, 2001), this thesis proposes that the SNARC effect in fact involves both the allocentric and the egocentric spatial reference frames. Several assumptions regarding the SNARC effect were specified in terms of constraints involving the alignment of the two types of reference frames. These assumptions were then tested in three experiments. In Experiment 1, a SNARC effect was found for a learned sequence that was associated with increasing perceptual magnitudes and not for other learned sequences involving magnitude information that were either decreasing in size or completely absent. This result indicates that the sequence needs to have a salient intrinsic directionality in order for a SNARC effect to occur. In Experiment 2, the SNARC effect disappeared when its allocentric and egocentric composites were dissociated from each other through imagery and response codes alignment manipulations. Namely, a standard SNARC effect was found for the horizontally aligned allocentric and egocentric axes. As for the vertically aligned axes, a gender effect was unexpectedly found where only the male participants displayed a SNARC effect. Finally, in Experiment 3, it was demonstrated that the allocentric and egocentric axes should overlap at their subjective midpoint of the former and midline of the later in order for the SNARC effect to occur. The results showed that new associations of the response codes with left and right were formed depending on the position of the midpoint standard within the sequence. These experiments contribute to the understanding of the SNARC effect by presenting it as an effect of the interaction of multiple allocentric and egocentric spatial representations. |
