Impairments of the mental number line for two-digit numbers in neglect

Humans represent numbers along a left-to-right oriented Mental Number Line (MNL). Neglect patients seem to neglect the left part of the MNL, namely the smaller numbers within a given numerical interval. However, until now all studies examining numerical representation have focussed on single-digit numbers or two-digit numbers smaller than 50. In this study, the full range of two-digit numbers was assessed in neglect patients and two control groups. ipants were presented with number triplets (e.g., 10_13_18) and asked whether or not the central number is also the arithmetical middle of the interval. The factors manipulated were decade crossing (e.g., 22_25_28 vs 25_28_31), distance to the arithmetical middle (e.g., 18_19_32 vs 18_24_32), and, most importantly, whether the central number was smaller or larger than the arithmetical middle (e.g., 11_12_19 vs 11_18_19). Neglect patients differed from controls in that they benefited less when the middle number was smaller than the arithmetical middle of the interval. t patients thus seem to have particular problems when accessing the left side of numerical intervals, also when adjusted to two-digit numbers. Such an impaired magnitude representation in neglect seems to have detrimental effects on two-digit number processing as the helpful spatial metric of magnitude cannot be properly activated.