**5. Conclusions**

Previous research on the relation between MA and P3 latency has been rather inconclusive reporting negative correlations [25,29,30,33], positive correlations [28] or no significant correlations at all [22,27]. The present study provided first evidence for the notion that task demands on selective attention play a crucial role for the expected negative functional relationship between MA and P3 latency, as proposed within the conceptual framework of the mental speed approach. The negative relation between MA and P3 latency increased systematically with an increase of selective attention required by the task used to elicit the P3 component. As P3 latency and RT were functionally independent from each other, the failure to obtain a relationship between RT and MA did not necessarily hamper the interpretation of the relation between MA and P3 latency.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2076-3425/9/2/28/s1, Figure S1: Grand averages (solid lines) and standard deviations (dotted lines) of the event-related potentials in the three CPT conditions; Figure S2: Grand average (solid line) and standard deviation (dotted line) of the event-related potentials in the CPT0 condition; Figure S3: Grand average (solid line) and standard deviation (dotted line) of the event-related potentials in the CPT1 condition; Figure S4: Grand average (solid line) and standard deviation (dotted line) of the event-related potentials in the CPT2 condition.

**Author Contributions:** S.J.T., S.M., and T.H.R. conceived of and designed the experiment. S.M. set up and performed the experiment. T.K. prepared and analyzed the data. T.K. and S.J.T. wrote the paper. All authors reviewed and edited the paper.

**Funding:** This research received no external funding.

**Acknowledgments:** We thank Annkathrin Müller, Christine Krebs and Dominic Freitag for their help in collecting and preparing data.

**Conflicts of Interest:** The authors declare no conflict of interest.
