When a monkey searches for a colour and orientation feature conjunction target, the scan path is guided to target coloured locations in preference to locations containing the target orientation [Vision Res. 38 (1998b) 1805]. An active vision model, using biased competition, is able to replicate this behaviour. As object-based attention develops in extrastriate cortex, featural information is passed to posterior parietal cortex (LIP), enabling it to represent behaviourally relevant locations [J. Neurophysiol. 76 (1996) 2841] and guide the scan path. Attention evolves from an early spatial effect to being object-based later in the response of the model neurons, as has been observed in monkey single cell recordings. This is the first model to reproduce these effects with temporal precision and is reported here at the systems level allowing the replication of psychophysical scan paths.