1 Department of Experimental Psychology, University College London (UCL), 26 Bedford Way, London WC1H 0AP, UK; dunnhumby Ltd., 184 Shepherd's Bush Road, London W6 7NL, UK.
2 dunnhumby Ltd., 184 Shepherd's Bush Road, London W6 7NL, UK.
3 The Alan Turing Institute, 96 Euston Road, London NW1 2DB, UK; Department of Experimental Psychology, University College London (UCL), 26 Bedford Way, London WC1H 0AP, UK.