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a large increase in striatal dopamine level) that is required for attentional perception of this
stimulus.
Experimental data suggest that at least for low-level tasks each of visual and auditory
modality is under separate attentional control, rather than under a supramodal attentional
control (Alais et al., 2006). We suppose that this effect could be the consequence of
processing the diverse features of visual and auditory information in different C-BG-Th-C
loops. Since different populations of dopaminergic cells project to striatal loci connected with
low-order visual and auditory cortical areas attentional influencing visual and auditory
processing could be independent. The same mechanism can underlie commonly known
distinction between object and spatial attention that reflects the organization of visual cortex
into parallel “what” and “where” processing streams. We assume that object attention could
be performed by C-BG-Th-C loop, which includes inferotemporal cortex, whereas spatial
attention could be performed by C-BG-Th-C loop, which includes parietal cortex. This
assumption is based on the data that mentioned cortical areas categorizes, respectively, what
objects are in the world and where these objects are in space (Goodale and Milner, 1992).
It is known, that new unexpected stimuli involuntarily capture attention thus increasing
neocortical responses. However even new objects do not attract attention unless they created a
strong local changes (Franconeri et al., 2005). From our model follows, that only strong
stimulus could switch on attention since only it can lead to discharges of striatonigral cells
and thus provide disinhibition of the SC, which activates dopaminergic cells (Fig. 2).
According to experimental data, at least some different processes are involved into
involuntary and voluntary attention (Fu et al., 2005). From our point of view, this difference
could be the consequence of diverse pathways for dopaminergic cells excitation.
It was found that disruption of connections between medial PfC and STN or bilateral
STN damage lead to attentional deficiency (Chudasama et al., 2003). On the contrary, high-
frequency stimulation of STN neurons improved attention in parallel with dopamine
medications (Brusa et al, 2001). Known models do not explain mechanisms of these effects,
whereas it is directly follows from our models that STN activated by the PfC is necessary for
attention since it directly excites dopaminergic cells (Fig. 2).
It was shown that the attention strengthens the binding of asynchronously perceived
properties of stimulus due to acceleration of processing of each of these properties whereas
perceptual asynchrony between attributes remains constant across attended and unattended
conditions (Paul and Schyns, 2003). In the view of our model, this asynchrony remains
constant because processing of different properties of stimulus is performed mainly in the
separate C-BG-Th-C loops and in each loop dopamine promotes acceleration of processing
due to reduction of number of circulation for selection of neural representation of each
attribute of stimulus.
If the two stimuli share properties, processing of the second stimulus is more efficient
than of a similar stimulus not preceded by the first stimulus (Dehaene et al., 1998). This
typical attentional priming situation was explained by a short-term or iconic memory trace.
Due to existence of such trace, activity of firstly excited neocortical neurons could be
additionally amplified by C-BG-Th-C loop in comparison with none activated neurones.
However, continued training abolishes the attentional effect (Chirimuuta et al., 2007). From
point of view of our model, this abolishment could be the result of decrement and subsequent
disappearance of responses of dopaminergic cells on repeating stimuli (Schultz, 1993).
