The influence of the place-value structure of the Arabic number ...

4 blocks of 40 trials each, which the participant initiated by pressing one of the response keys.
Trial order was randomized for each participant.
Before each trial a fixation cross was presented in the centre of the screen for 500ms.
Then the three numbers were presented for 15,000 ms followed by a ISI of 5,000 ms. The
experiment took approximately 15 to 25 minutes, depending on how long participants rested
between blocks.
RESULTS
For statistical analyses RT and error data were used. Only RTs followed by a correct
response were considered for further analysis. A trimming procedure eliminated trials with
RTs shorter than 200 ms and longer than 15,000 ms and – in a second step – RTs outside +/- 3
SD of each participant’s individual mean. In total 92.33 % of all trials fulfilled these criteria
and were used for further analyses. As stroke patients show a greater variability in their RTs
than healthy participants, a z-transformation on individual item RT, using the mean and
standard deviation per participant for standardization, was carried out. Error rates were arcsine
transformed prior to the analyses. There was no speed accuracy trade-off present in our data
as indicated by the absence of a reliable negative correlation of error rate and RT in any item
condition (all r > - .40, all p > .10, N = 18).
The main interest of the current study was to contrast patients suffering from neglect and
those without neglect in terms of their performance in the NBT. Therefore, the two control
groups (patient controls and healthy controls) were pooled into one group for the main
analyses of this study. For the interested reader Appendix B reports all results separated for
the single control groups. As neglect patients do not only neglect the left side of space but
also the left parts of numerical intervals (e.g. Zorzi et al., 2002), processing numbers on the
left side of a numerical interval (i.e. the central number being smaller than the arithmetical
middle of the interval) should be relatively more impaired.
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