Attention

Squire et al Ch 48

Can you elaborate more on statistical decision theory for control of movement by giving an example? Prior: P(state)-memoryLikelihood: P(data|state)-sensory dataPosterior: P(state|data)(a) In an example of movement control, is state the desired position, data the current position? So the nervous system would try to compute the posterior: given current position, what's the probability of desired position. (b) I wonder how is this posterior implemented in motor system, and where could this be computed.(c) What's the role of loss function?

What is the timeline for developmental plasticity for learning movements? Are there clear points in childhood and/or adolescence where plasticity greatly decreases?

1). About visuomotor plasticity in development: are there any motor skills that must be learned in early childhood, that otherwise would be extremely difficult to learn in adulthood? And why? (phoneme pronunciation? basketball tricks?)2). Attention and gaze. When the subject is blanking/absent-minded, How does his/her gaze look like? Any fixation? Especially in driving.

1. The strength of Fitt’s law and the plasticity of the visuo-motor system seems contradictory. I would expect that Fitt’s law could be easily violated with training. Or, is it unlikely to see improvement in basic movements like moving the hand forward on a single plane? 2. Regarding eye-hand coordination, while watching shoppers remove items from a shelf, the hand closely follows the eyes until the actual moment of grasping the object. As the hand approaches the target the eyes tend to focus in another location, usually directly forward in the field-of-vision. The hand movements are generally successful without the overt visual attention. Could this be evidence of “reverse covert attention”? Meaning that the eyes have moved overtly, yet the visual system is covertly still on the last position to help guide the hand?

It is commonly believed that seeing a word, for a native speaker, activates comprehension, implying that attention is automatic. Are there ways of isolating the region or regions associated with the conceptual response to visual stimuli. For example words vs. nonsense words or drawing of animals with specific common names vs. nondescript.

Visuo-motor coordination; Held & Hein

Language learning: critical period??? Production and perception.

Motor skills: Rosenbaum – performance depends on practice.

Attention is a hypothetical internal variable with limited/no explanatory power.

Central idea: selection – of stimulus and action

Also: resource limitations – not necessarily a problem, but an inevitable aspectof goal directed behavior. Ie it wouldn’t help if we were able to process more information – however, learning allows more compact codes.

Potential role of basal ganglia:

Spatial Neglect: lesions of parietal lobe, the frontal lobe, anterior cingulate cortex-profound inability to attend to certain spatial regions

Subcortical level - lesions of the basal ganglia or of the pulvinarthalamic nucleus, which is heavily connected with the parietal cortex

Not sensory or motor: failure to select – therefore thought of as attentional deficit.

Neglect may be object centered (above), eye centered, gaze centered, or body centeredAffects imagined images.

Extinction: image on good side suppresses image on bad side

Note other disorders of attention: schizophrenia (disordered eye movements), ADD

Fronto-parietal network: FEF (frontal eye fields), SEF (supplementary eye fields, and SPL (superior parietal lobule) Note similarity of areas involved in eye movements and attention. Note also, not just spatial attention but attention to objects and features.

Feedback from fronto-parietal network affects responses of cells in visual cortex.

Event related potentials ERP’s evoked in visual cortex recorded on scalp when attending right or left

Fronto-parietal attentional control system (LIP/FEF)

Cells in LIP do not respond to steadystimuli

Cells respond to behaviorally relevant stimuli

LIP cell responses modulated by reward towards

away

LIP cell responds when relevant cue isin receptive field and when left handis used.Ie modulated by task and hand

Different reward probabilities

Summary: multiple influences on goal (attentional) selection in LIP

Microstimulation of FEF modulates response to visual stimulus in V4

Response of a single V4 neuron with (gray) and without (black) FEF microstimulation

Has attention been shown to affect background spike rate (i.e decreasing noise and increasing the contrast of a response to the stimulus) or just to increase the magnitude of the response to the attended stimulus?

Do I understand correctly that attention is thought to bias the responses in the visual pathway as low as V1 and LGN?

LGN receives input from multiple sources including striate cortex, the thalamic reticular nucleus (TRN), and the brain stem. (plus retina)The LGN therefore represents the first stage in the visual pathway at which cortical top-down feedback signals could affect information processing.

fMRI expts show attentional modulation of LGN (even stronger than attentional effects in early visual areas.

Attentional capture or popout

Where are the bottlenecks? What is the nature of the limitation???

Bayesian Approach:

Cueing effect in Posner paradigm without enhanced processing at attended location.Eckstein et al, 2002.

Greater prior liklihood of stimulus at cues location leads tobetter performance (detectability).

Classification Image Technique:

Subject detects a signal in noiseSort out the False Alarm trialsAdd all the images that resulted in false alarmsReveals the information that led to a false alarm.Cf reverse correlation technique

Search Templates

Simulation results using classification images

Classification images from simulations using differentfilters in cued and uncued locations.

Classification images from subjects in Posner experiment.

Supports Bayesian interpretation of performance, not use of different filters in cued and uncued locations.

Biased competition

What is attention?-Capacity to select information from the environment and select actions to perform

Substantial overlap between circuitry for eye movements and circuitry for spatial attention.

Parietal – frontal network influences visual cortical areas including V1.

LGN may gate incoming visual signals.

Attention appears to act in a way that biases competition between stimuliwithin a receptive field.

Attention is limited - why?Limitations may derive from multiple levels of processing in the brain eg sensory, motor, and sub-cortical circuitry such as basal ganglia.

Change Blindness: insensitivity to changes in visual scenes madeduring an eye movement/transient occlusion.

Change blindness challenges idea that perception delivers acomprehensive representation of world.

What is represented? Attended objects/regions of central interest?