Visual indexing theory
It proposes a pre-attentive mechanism (a ‘FINST’) whose function is to individuate salient elements of a visual scene, and track their locations across space and time.
As those objects move about, your fingers stay in respective contact with each of them, allowing you to continually track their whereabouts and positions relative to one another.
"Thus distal features which are currently projected onto the retina can be indexed through the FINST mechanism in a way that is transparent to their retinal location.
Once it has been allocated a FINST, the index provides the visual system with rapid and preferential access to the object for further processing of features such as colour, texture and shape.
In terms of an analogy offered by Posner, Snyder and Davidson (1980): "Attention can be likened to a spotlight that enhances the efficiency of detection of events within its beam".
He argues that a pre-attentive mechanism is needed to individuate objects upon which a spotlight of attention could be directed in the first place.
Furthermore, results of multiple object tracking studies (discussed below) are "incompatible with the proposal that items are accessed by moving around a single spotlight of attention.
It is these descriptions, and not the raw content of our visual perceptions, that allow us to construct meaningful representations of the world around us, and determine appropriate courses of action.
In Pylyshyn's words, "it is not the bright spot in the sky that determines which way we set out when we are lost, but the fact that we see it (or represent it) as the North Star".
Successful completion of the task thus requires subjects to continually track each of the target objects as they move, and ignore the distractors.
Results Under such experimental conditions, it has been repeatedly found that subjects can track multiple moving objects simultaneously.
Numerous studies (dating back to Jevons in 1871)[19] have demonstrated that subjects can very quickly and accurately report the quantity of objects randomly presented on a display, when they number fewer than around five.
While larger quantities require subjects to count or estimate — at great expense of time and accuracy — it seems that a different enumeration method is employed in these low-quantity cases.
[20] In 2023 a study of single neuron recordings in the medial temporal lobe of neurosurgical patients judging numbers reported evidence of two separate neural mechanisms with a boundary in neuronal coding around number 4 that correlates with the behavioural transition from subitizing to estimation, supporting the old observation of Jevons.
[21][22] Experimental setup In a typical experiment, subjects are briefly shown (for around 100ms) a screen containing a number of randomly arranged objects.
In other words, the subsets "could, in a number of important ways, be accessed by the visual system as though they were the only items present".
[7] Furthermore, the subsetted objects' particular positions within the display made no difference to subjects' ability to search across them — even when they were distally located.
[26] These results are consistent with the predictions of visual indexing theory: FINSTs provide a possible mechanism by which the subsets were prioritised.
