Introduction definition of the construct a bit of history Spatial attention and early vision contrast spatial resolution some experimental methods Feature based attention Visual search Attention

Helmholtz on covert attention (1867) “It is a curious fact, by the way, that the observer may be gazing steadily at the two pinholes and holding them in exact coincidence, and yet at the same time he can concentrate his attention on any part of the dark field he likes, so that when the spark comes, he will get an impression about objects in that particular region only. In this experiment the attention is entirely independent of the position and accommodation of the eyes, or indeed, of any known variations in or on the organ of vision. Thus it is possible, simply by a conscious and voluntary effort, to focus the attention on some definite spot in an absolutely dark and featureless field. In the development of a theory of the attention, this is one of the most striking experiments that can be made.” (Physiological Optics, Vol, 3, p Thoemmes Press Ed.)

What is attention? Why? Two primary themes characterize attention: Perceptual gating (selection) Conscious perception is always selective, but selection is not always conscious Capacity limitation Our limited ability to carry out various mental operations at the same time

early selection - physical characteristics of messages are used to select one message for further processing and all others are lost (Broadbent, 1958) attenuation - physical characteristics are used to select one message for full processing and other mes- sages are given partial processing (Treisman, 1964) late selection - all messages get through, but only one response can be made (Deutsch & Deutsch, 1963) Competing hypothesis

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When does the selection take place? Classic Theory I. Early Selection Filter theory proposed by Broadbent (1958) Because of our limited ability to carry out multiple discriminations in parallel, only physical featural analyses can be carried out in parallel. Counterevidence: findings of divided-attention studies People are capable of fairly extensive parallel processing. Ex. Letter search tasks

Early selection – selection is based on physical properties of the stimulus (e.g., pitch, loudness) Only one input channel can be processed at a time Semantic interpretation only after selection Conscious control It takes time to shift attention Broadbend‘s filter theory (1958)

When does the selection take place? Classic Theory II. Late Selection Proposed by Deutsch (1963) Perceptual analysis operates without capacity limitations and without voluntary control. Counterevidence: Inattentional Blindness Divergence of ERPs (Event-related potentials) very early after presentation of a stimulus.

Late selection Attended Channel: THE GIRL WAS dogs, six, beach... Unattended Channel: world, eight, WAITING FOR HER... Reported: THE GIRL WAS WAITING FOR HER...

Sperling (1960) partial report An array of letters (three rows of four) was flashed briefly In whole report, the observer recalled as many letters as possible, ~ 4. In partial report, a high, medium, or low tone, presented after the offset of the array, indicated that the letters in only the top, middle, or bottom row were to be reported, ~7 Observers can selectively encode into memory a spatially defined subset of the array—an act of spatial selective attention

Spatial attention: the selective processing of information at a given location. Posner, Nissen, & Ogden (1978)

Attention plays a key role in perception 1980s and early 90s: necessary for effortful processing ‘glue’ that binds simple features into an object what attention does? what processes does it affect? last decade, effects of attention on perception: psychophysics single-unit recording neuroimaging

Limited resources The high-energy cost of neuronal activity involved in cortical computation limits our ability to process information: constant overall energy consumption available to the brain neuronal metabolic cost depends on the spike rate the cost of a single spike is high average discharge rate of active neurons will determine how many neurons can be active concurrently […1%! ] The brain needs machinery for the system to allocate energy according to task demand… selective attention. Lennie, Current Bio ‘03

Selective Attention … the amount of information coming down the optic nerve - estimated to be in the range of 10 8 ~ 10 9 bits per second - far exceeds what the brain is capable of fully processing and assimilating into conscious experience … C. Koch (2004) Selective Attention (processing input preferentially) is the natural strategy for dealing with this bottleneck.

Selective Visual Attention Capacity Limitation As visual information traverses the successive cortical areas of the ventral visual stream, the size of receptive fields increase. Neurons in higher order areas with large receptive fields have to deal with many visual stimuli that appear simultaneously within their receptive fields. This is why the neurons which make up the visual system are limited-capacity channels.

Visual attention facilitation and selection of information overt attention - head and eye movements covert attention - monitor the environment inform eye movements

sustained transient endogenousexogenous controlled reflexive goal-drivenstimulus-driven 300 ms ms corticalalso subcortical feedback ? Spatial covert attention

Campbell & Robson (1968)

Spatial Frequency (cpd) Sensitivity (1 / Threshold) Contrast sensitivity function

Attention enhances sensitivity Attention enhances sensitivity neutral peripheral 1 cpd 2 cpd 4 cpd8 cpd Carrasco, Penpeci & Eckstein, Vis.Res. 2000

modified Naka-Rushton function; N = attentional parameter Martinez-Trujillo & Treue ’02

Ling & Carrasco, Vis. Res. 2006

Attention increases signal intensity Intensity increases and lengthens adaptation Does the enhanced signal due to sustained attention lead to a stronger, longer-lasting adaptation effect? Sustained attention & adaptation

Contrast thresholds Time Fixation 1000 ms. Adapter: 50% contrast; counter-phase flicker (9 Hz) sustained neutra l Cue + Adapter 50 ms -16 s.. ISI 100 ms. Target 100 ms. 2AFC orientation discrimination task (±3°) Response 1500 ms. Adapt recovery 50 ms - 16 s. response cue

Contrast threshold over time Ling & Carrasco, Nature Neurosci 2006

Attentional effect: neutral / attended threshold Enhancement Impairment Ling & Carrasco, Nature Neurosci 2006

Attention benefit and cost Ling & Carrasco, Nature Neurosci 2006

Sustained attention and adaptation Attention increases contrast sensitivity The attention state modulates adaptation: enhanced signal strengthens adaptation, impaired sensitivity over time; diminished signal weakens adaptation, improved sensitivity over time Ling & Carrasco, Nature Neurosci 2006