Data analysis In order to measure the amount of temporal bias observed in each condition, the individual frequencies of ‘‘longer’’ responses were converted into probabilites and a logistic model was fitted to the data of each participant as a function of the duration of the test stimulus (from 150 to 450 ms). This allows to determine the subjective ‘‘bisection point’’ for each condition. This point represents the time interval for which the observer perceives the duration of reference and test stimuli as equal, and is computed as the time interval at which ‘‘longer’’ and ‘‘shorter’’ responses are reported equally often (more specifically when p(‘‘longer’’ response = .5). A shift in the References 1. Meck WH, Church RM (1983) A mode control model of counting and timing processes. Journal of Experimental Psychology: Animal Behavior Processes 9(3): 320–334. 2. Roberts WA (1995) Simultaneous numerical and temporal processing in the pigeon. Current Directions in Psychological Science 4: 47–51. 3. Roberts WA, Mitchell S (1994) Can a pigeon simultaneously process temporal and numerical information? Journal of Experimental Psychology: Animal Behavior Processes 20: 66–78. 4. Dormal V, Seron X, Pesenti M (2006) Numerosity-duration interference: a Stroop experiment. Acta Psychologica 121(2): 109–124. 5. Roitman JD, Brannon EM, Andrews JR, Platt ML (2007) Nonverbal representation of time and number in adults. Acta Psychol (Amst) 124(3): 296–318. 6. Meck WH, Church RM, Gibbon J (1985) Temporal integration in duration and number discrimination. Journal of Experimental Psychology: Animal Behavior Processes 11(4): 591–597. 7. Buhusi CV, Meck WH (2005) What makes us tick? Functional and neural mechanisms of interval timing. Nature Reviews Neuroscience 6(10): 755–765. 8. De Long AJ (1981) Phenomenological space-time: towards an experiential relativity. Science 213: 681–683. 9. Johnston A, Arnold DH, Nishida S (2006) Spatially localized distortions of event time. Curr Biol 16: 472–479. 10. Morrone MC, Ross J, Burr D (2005) Saccadic eye movements cause compression of time as well as space. Nat Neurosci 8: 950–954. Mental Time Number Line bisection point in either direction indicates a temporal bias in the corresponding experimental condition. A paired-t-test was then performed on the individual bisection points to compare the amount of temporal bias in each condition. Author Contributions Conceived and designed the experiments: GK CC CV MO. Performed the experiments: CV MO PP. Analyzed the data: PT MO. Wrote the paper: PT MO. 11. Walsh V (2003) A theory of magnitude: common cortical metrics of time, space and quantity Trends Cogn Sci 7(11): 483–488. 12. Droit-Volet S, Clement A, Fayol M (2003) Time and number discrimination in a bisection task with a sequence of stimuli: a developmental approach. Journal of Experimental Child Psychology 84(1): 63–76. 13. Fischer MH, Castel AD, Dodd MD, Pratt J (2003) Perceiving numbers causes spatial shifts of attention. Nat Neurosci 6: 555–556. 14. Lewis PA, Miall RC (2006) Remembering the time: a continuous clock. Trends Cogn Sci 10(9): 401–406. 15. Dehaene S, Bossini S, Giraux P (1993) The mental representation of parity and numerical magnitude. Journal of Experimental Psychology: General (122): 371–396. 16. Rusconi E, Kwan B, Giordano BL, Umilta` C, Butterworth B (2006) Spatial representation of pitch height: the SMARC effect. Cognition 99(2): 113–129. 17. Gevers W, Reynvoet B, Fias W (2003) The mental representation of ordinal sequences is spatially organised. Cognition 87(3): B87–B95. 18. Vicario CM, Caltagirone C, Oliveri M (2007) Optokinetic stimulation affects temporal estimation in healthy humans. Brain and Cognition 39: 1317–1328. 19. Vallesi A, Binns MA, Shallice T (2008) Spatial temporal association of response codes effect: understanding cognitive representation of time. Cognition doi:10.1016/j.cognition.2007.10.011. 20. Burr D, Tozzi A, Morrone MC (2007) Neural mechanisms for timing visual events are spatially selective in real-world coordinates. Nat Neurosci 10(4): 423–425. PLoS ONE | www.plosone.org 4 March 2008 | Volume 3 | Issue 3 | e1716