12 Attention and Consciousness The breath of the mind is attention – Joseph Joubert

Auditory attention – Cocktail party effect

Binaural processing Audio attention can be allocated to a sound source in space. Keyword detection Immediately capture “important” words originated from unattended stimuli Selective attention Focusing on a particular conversation while ignoring others

What is attention for? Our brains have limitations on the ability to simultaneously carry out multiple cognitive or perceptual tasks The limitations reflect the limited capacity of some stage or stages of sensory processing, decision-making, or behavioral control. As a result of such computational bottlenecks, it is necessary to have neural mechanisms in place to ensure the selection of stimuli, or tasks, that are immediately relevant to behavior. “Selective attention” is a broad term denoting the mechanisms that mediate this selection. It is possible to focus on selected stimuli in any sensory modality—sights, sounds, smells, and touch.

Broadbent’s model of selective attention

Early versus late selection of information processing Perhaps unattended channel information was not completely gated from higher analysis but was merely degraded or attenuated

Varieties of attention Overt vs. Covert We look at an object when we overtly direct our attention to it. However, it is also possible to attend covertly to objects without looking directly at them. Covert attention improve peripheral visual acuity, thereby extending the functional field of view. Top-down vs bottom-up Bottom-up attention: exogenous or stimulus driven Top-down attention: based on internally defined goals and against potential external distractions

Voluntary attention (Top-down) Endogenous cuing “Spotlight”

Reflexive attention (bottom-up) Exogenous cuing Responses are faster to targets at the cue location, but only for a short time ( ms) The effect is reversed when the time between the task-irrelevant cue and the target is more than 300 ms -> Inhibitory aftereffect or inhibition of return

Pop-out search and conjunction search

Many studies supported the theory that limited capacity results from information processing bottlenecks that occur relatively late in processing, after features are already integrated into wholes. One possibility is that the bottleneck occurs when objects enter a limited capacity working memory. Under this view, attention plays the role of selecting which objects pass through the bottleneck. The computational bottleneck in search tasks

Balint’s syndrome A severe disturbance of visual attention and awareness Only one or a small subset of available objects being perceived at any one time Balint’s syndrome informs us about the nature of the attention and awaremess

The latency of the peak < 90 ms -> Supporting the early- selection models Steven Hillyard et al 1973 experiment

Woldorff and Hillyard (1991) experiment: P20-50 effect Woldorff and Hillyard (1993) experiment: MEG (magnetoencephalogram) The M20-50 effect was localized to the auditory cortex in Heschl’s gyri

Neurophysiology of voluntary visual attention

This P1 attention effect (70-90 ms) is only reliably found in spatial attention, not on other visual features (color, shape, etc). The attentional effect of more complex features were observed later in the ERPs (>120 ms)

The first volleys of afferent inputs into striate cortex (V1) take place with a latency longer than 35 ms. Numerous studies showed that the P1 attention effect are generated in extrastriate cortex As for the auditory selective attention, selective visual attention effect takes place early in visual cortex.

Reflexive cuing task

Spatial attention and visual search Question: Spatial attention precede feature/object attention Or Feature attention leads spatial attention?

Feature and spatial attention In general, spatial attention produces the shortest-latency ERP A host of feature-based ERP comes with slightly longer latencies. N2pc -> a response indexes how attention zooms down to focus on objects in visual space in a search task Max Hopf et al 2004 experiment showed that 1. feature selection ERP in ventral occipitotemporal cortex with 140 ms latency. 2. N2pc follows in 30ms in more anterior regions

We now understand that spatial attention influences the processing of visual inputs Attended stimuli produce greater neural responses than do ignored stimuli The difference is observed in multiple visual cortical areas But, two questions come to mind: 1.Are such effects limited to visual cortical processing, or might they begin earlier in the subcortical relays? 2.What does attention do for the brain to permit the attended signal to exert a greater control on perception and awareness John Duncan and Robert Desimone proposed a biased competition model for selective attention.

Summary of early neuroimaging attention studies using position emission tomography (PET) by Corbetta and colleagues (1991), Heinze and colleagues (1994), and Mangun and colleagues (1997).

Nonspatial attention modulates sensory cortices Studies found: Attention to shape and color led to response enhancement in regions of the posterior portion of the fusiform gyrus, including area V4. Attention to speed led to response enhancement in areas MT/MST. Attention to faces or houses led to response enhancement in areas of the mid anterior portion of the fusiform gyrus, areas responsive to the processing of faces and objects.

Desimone and associates studied the effect of selective attention on the responses of a neuron in area V4 of macaque monkeys

V1 and V2 neurons showed similar effects

Fecteau, J. H. and Munoz, D. P. Nat. Rev. Neurosci. 4 (1-9), 2003 Frontal and parietal cortices play roles in visual attention LIP: lateral intraparietal area FEF: frontal eye field SEF: supplementary eye field DLPFC: dorsal lateral prefrontal cortex

Role of frontal and parietal cortices – fMRI studies Brain areas in the parietal, frontal, and cingulate cortices are especially active in relation to spatially directed attention. SPL: superior parietal lobule FEF: frontal eye field SEF: supplementary eye field

Neuronal receptive fields – Possible source of limitation? The sizes of receptive fields increase from less than a degree of visual arc in primary visual cortex (area V1) to about 20° of visual arc in area TE, the last purely visual area in the ventral visual processing stream Therefore, a likely explanation for why one cannot process many different objects in a scene simultaneously is that neurons, whose signals are limited in bandwidth, cannot simultaneously send signals about all the stimuli inside their receptive fields. This idea implies that processing limitations exist at all levels of processing but that they become more pronounced in higher order visual areas, where receptive field sizes are larger. Think of a corporation again!

Neglect syndrome: A deficit of spatial attention Unilateral lesions in the parietal lobe, the frontal lobe, and the anterior cingulate cortex (Heilman, 1979; Vallar, 1993) in humans may cause a profound inability to attend to certain spatial regions, a syndrome known as spatial neglect. Neglect patients may be reluctant to initiate movement in contralesional space, with or without external sensory stimulation. Neglect patients have normal vision in the contralesional visual field once their attention has been directed there, and they have no hemiparesis that could account for their reluctance to move.

In severe cases, patients with neglect behave as if the world contralateral to their lesioned hemisphere (the contralesional world) has ceased to exist. Neglect syndrome: A deficit of spatial attention

Different forms of neglect correlate with dysfunction in different brain regions Lesion in inferior parietal lobule and temporoparietal junction -> neglect for extrapersonal space Lession in superior temporal gyrus -> object-based neglect

Visual recollections of two ends of an Italian piazza by a neglect patient