Experiments on the dynamics of attention: Perception of visual rhythm and the time course of inhibition of return in the visual field

How attention is controlled is one of the challenging topics in
cognitive neuroscience and psychology. For spatially represented
targets in the visual field it has been shown that some features of
visual stimuli like different colors instantaneously ‘pop-out’,
while others require a serial search which is conceived of as an
effortful task. It is an open question whether dynamic feature of a
stimulus are processed instantaneously without high attentional
demand or serially with high demand. This question was studied in
experiments on rhythm perception with periodically moving stimuli,
and a visual search paradigm was employed. The search display
consisted of vertically moving dots with regular rhythms; one dot
however moved with a different period, and this dot with a longer
or shorter period had to be detected as fast as possible. To make
the period of the movement a critical target, amplitudes and phases
of the distractors were randomized. It was observed that the
perception of a visual rhythm defined only by the period does not
lead to a pop-out effect. Apparently, the conjunction of period,
equal phase and equal amplitude of movements are necessary for an
effortless processing of visual rhythms. Interestingly, a faster
rhythm compared to the distractors was detected with shorter
reaction times. In additional experiments, it was for instance
shown that auditory information supports the extraction of rhythmic
visual targets indicating an intermodal mechanism. In another
experimental set-up it was tested whether the attentional machinery
is controlled by a common temporal mechanism. Experiments on
‘inhibition of return’ (IOR) have indicated that attentional
control in the peri-foveal region of the visual field underlies a
different neuronal mechanism compared to the periphery of the
visual field. This eccentricity effect of IOR raises the question,
whether attentional control for the visual periphery is
characterized by a longer time constant as the peripheral
inhibitory control is much stronger. Experimental evidence
indicates, however, that the two attentional systems share the same
time window of approximately three seconds. These observations
support the notion of a functional subdivision of the visual field
which is overcome, however, by a common temporal control mechanism.