Hi,

eye-Tracking is the most feasible and realiable way to define detection of a target in a visual search paradigm. Detection is defined as overlap of target location and fixation location. Usually, visual search performance is measured by time to target fixation or percentage of correct detections. Theoretically, you would not need to save eye-movement trace, if you have time stamps of target onset and fixation-on-target. However, there is no extra cost to save the eye-movement data, as it is provided by the raw data stream of an eye tracker.

Furhter reference: Gliga, T., Bedford, R., Charman, T., Johnson, Mark H., Baron-Cohen, S., Bolton, P., . . . Tucker, L. (2015). Enhanced Visual Search in Infancy Predicts Emerging Autism Symptoms. Current biology, 25(13), 1727-1730. doi:http://dx.doi.org/10.1016/j.cub.2015.05.011

Dear all,

There are two main types of visual search paradigms as evaluated from the point of view of involvement of eye movements. First, overt search when subjects scan display(s) by eye movements and this is allowed and/or presupposed by the experimental paradigm used. Second, the covert search when the search field (with searchable objects included) remains spatially invariant with regard to eye fixation and subjects use covert spatial selective attention mechanisms. In the second version either display must be presented for such a short duration that subjects can not benefit (or challenged) from changing fixation; when they refocus eyesight somewhere else (not at the fixation point anymore), display has been switched off already. Now, most importantly, the dynamics of eye fixations and scanpaths are crucial to be taken into account and measured because visual spatial resolution considerably differs between foveal, parafoveal and peripheral parts of the visual field. If we do not know where the eye fixated during certain moments of visual display presentation, we do not know how well stimuli (especially their spatial-frequency information, but also color discrimination if lower luminances are used) can be or have been discriminated. This can lead to artefacts and to loss of important data for interpretations.

Cheers to all in 2018

Dear Qing He,

The answer to your primary question would be driven by the objectives of your research. In particular, is your research attempting to specifically address attention issues? As pointed out by Talis Bachmann in the preceding post, information processing within the brain is influenced by both covert and overt attention. It is often problematic to directly analyse covert processing, even if fMRI or EEG data is also being collected. However, overt attention is normally relatively easy to capture through various saccade tracking systems. This collected data can provide extremely useful insights, by providing direct information on:

(1) bottom-up (e.g. salience driven activations), which then drive neural processing and cognition; and

(2) top-down attention drivers (e.g. fixation due to cognitive attention drivers).

Such insights are best assessed by overlaying the saccades and fixations over the real-time screen content. However, the underlying data can also be quite useful for specific trend analysis (e.g. saccade distances in differing visual conditions, etc.). The insights that are exposed by the saccade and fixation data (which expose overt attention) can therefore be particularly important in assessing broader or specific implications.

For example, in some of my research, I have been assessing the implications of differing forms of visualisation on viewer comprehension and impressions. I can utilise tests and instruments that facilitate outcome assessment for these aspects. However, the eye tracking data shows the start of the processing into the afferent systems, and therefore delivers some highly useful insights into causative factors. In other words, capturing the overt attention can show the beginning point for processing, and this data can then be matched against the outcomes.

If you want to learn more about the implications of overt and covert attention and visual processing, have a look at Appendix 1 in Volume 2 of the thesis at: http://researchrepository.murdoch.edu.au/id/eprint/30198/ I hope that will be of help.

Wishing you all the very best,

Bruce Hilliard

Dear All,

I noticed when checking the preceding post that clicking on the link in the did not work. I am not sure why this is the case. You can, however, get to the file by cutting and pasting the link into your browser. I hope this will be of help.