Ocular measures of redundancy gain during visual search of colour symbolic displays

Sixteen observers participated in a visual search experiment in which colour coding, search type, and the amount of pre-search information available to the observers were varied. Observers searched simulated symbolic tactical displays to find the number of target symbols (i.e. exhaustive search) or the quadrant of the display in which a single target symbol was located (i.e. self-terminating search). Displays varied in the way in which the symbology was colour coded: colour was either relevant (i.e. redundant with symbol shape) or irrelevant (orthogonal to symbol shape), or the display was monochrome. Half of the observers were cued with regard to the coding scheme prior to display onset, while the other observers were not. There was no overall difference in search time or accuracy, number of eye fixations, or pupillary response between cued and non-cued observers, but only because cued and non-cued observers used the coding schemes differently. Redundancy gain was only evident for cued observers, who searched colour relevant displays faster and with fewer fixations than colour irrelevant or monochrome displays. Non-cued observers' search pattern did not differ across colour coding schemes, but they searched colour irrelevant and monochrome displays faster than the cued observers. Differences between cued and non-cued observers' search strategy are discussed with regard to their implications for design and evaluation of colour multipurpose displays.