Attentional control of saccades and short-term memory over time

Acronym: 
ASS
Term: 
2009-10 till 2012-10
Research Areas: 
B
Abstract: 

Humans direct their gaze to such locations where useful information may be found. Execution of eye movements is controlled by means of attention. A map of attentional priorities is in charge of ‘where-to-look-next’. Current theories assume that this map is cleared after each new snapshot (fixation) and that attentional priorities of previous fixations should not influence upcoming fixations. In a series of eye-tracking experiments we would like to investigate how visual attention and short-term memory control ‘where-to-look-next’ across eye movements. Implications of a short-term memory based model of attentional priorities are highly relevant for current theories of attention as well as for controlling mobile visual sensors.

 

Methods and Research Questions: 

Where-to-look-next?’ is a research issue of central interest for studying humans and for constructing efficient artificial intelligent systems with mobile visual sensors. Humans direct their gaze to such locations in space where useful information may be found. In a similar vein, intelligent technical systems with mobile sensors attempt to shift their cameras to potentially informative locations of the environment.

Converging evidence from experimental psychology and neuroscience has shown that the human/monkey eye is controlled by a visual attention mechanism (e.g., Deubel & Schneider, 1996). Visual attention selects a location in space and this location serves as the next landing point of the eye. Thus, knowing the task-dependent mechanisms of attentional control implies to know the mechanisms of ‘where-to-look-next’. Current theories of attentional control in vision share the common assumption of an attentional priority map (APM). An APM is a control map that gates computation of visual information in various feature maps, coding the position of objects and the priorities for allocating attentional resources. The location with the highest priority is also the target of the next eye movement. After attention/eye has been shifted towards a location in space this location within the APM will be inhibited in order to prevent reinspection. This so called ‘inhibition of return’ mechanism is the only memory component of current attentional theories. In other words it is assumed that attentional priorities are computed from scratch at the beginning of each eye fixation. Priorities from previous eye fixations (n-1, n-2... n-x) should not be stored and therefore should not influence computation of attentional priorities of the current eye fixation (n) (Wolfe, 1994; Itti & Koch, 2001). This is being assumed although research from the last years has shown strong interrelations between visual short-term memory and attention.

By combining psychophysical methods and state of the art eye-tracking we are seeking to understand the selection mechanisms that mediate access to short-term memory, and thus efficiently control ‘where-to-look-next’ in humans.

 

Outcomes: 

Saccades direct the part of the eye with the highest resolution – the fovea – to relevant locations/objects. More often than not the actual landing position of a saccade deviates from the intended landing position.  In a current line of experiments we addressed two related questions. First, is the deviation between intended and actual landing position compensated by visual attention, and second, are parameters for allocating attention computed anew after landing of the eyes?

We found that postsaccadic perceptual performance is best if an object is presented at the location to which the preceding saccade was aimed at, compared to locations 1° adjacent to the intended location. Importantly, the deviation of landing position did not influence perceptual performance. The current results suggest that spatial parameters for allocating attention presaccadically are maintained across saccades. Combined with an efference-copy signal of the eye movement this allows fast and accurate postsaccadic visual-spatial selection despite deviations of the actual from the intended saccade landing position.

 

Publications: