Psych 102 Lecture 6 Full Slides PDF

Preview

Summary

Download Psych 102 Lecture 6 Full Slides PDF

Description

Lecture'6:'Neural'mechanisms'of' object'perception,' Attention PSYC102 10/24/2017

Overview Brief'review' Neural'mechanisms'of'object'recognition,'ventral' visual'stream Attention'and'the'function'of'the'dorsal'visual' stream

2

Inverse projection problem: An image on the retina can be caused by an infinite number of objects.

The)Gestalt)laws)of)perceptual)organization Meaningfulness)or)Familiarity- Things'are'more'likely'to'form'groups'if'the' groups'appear'meaningful'or'similar.

Bev Doolittle (1984)

Symmetry and Convexity supports figure

Symmetry'(black)'vs.'Convexity'(white)'– bistable!

Object)recognition…very)hard)problem

Simple computational model: Recognition by Components (RBC) Biederman (1985) Geons (“Geometric'Ions”) Each'geon is'uniquely'identifiable'from'most' viewpoints'(viewpoint*invariant). Only'36'geons needed'to'make'thousands'of' objects. Objects'can'be'identified'if'the'geons can'be' identified:' which'geons are'present? what'is'the'spatial'relation'among'geons?

Structural-Description Models

Recognition by Components (RBC)

(a) It is difficult to identify the object behind the mask because its geons have been obscured. (b) Now that it is possible to identify geons, the object can be identified as a flashlight.

Recognition by Components

• Strengths – Viewpoint invariant – Represent 3-D structure

• Weaknesses – Complexity of representation – Doesn’t easily represent subtle metric differences (e.g., distance between eyes) – Recognition is at the level of categories (chair vs. table) rather than individuals (my office chair vs. my kitchen chair)

Summary • Brain'uses'basic'Gestalt'grouping'principles'to' organize'input • Computational'theories'like'RBC'can'help'to' explain'how'we'build'complex'objects'based' on'a'simpler'set'of'components'(but'its'not'a' complete'theory!)

14

How Does the Brain Process Information About Objects?

Visual)input)is)extremely)variable)– somehow)need)position/rotation)invariance((or) tolerance)

View'invariant'responses'to'familiar'objects'in'monkey'area'IT

The'neuron’s'responses'are'similar'within'each'object'across'viewpoints. Booth'and'Rolls,'1998

Viewpoint and size invariant responses – just signal the feature that you are tuned to

Single)unit)responses)in)area)TE)– very)stable)across)time!

Bondar'IV,'Leopold'DA,'Richmond'BJ,'Victor'JD,'et'al.'(2009)'Long-Term'Stability'of'Visual'Pattern'Selective'Responses'of'Monkey Temporal'Lobe' Neurons.'PLoS'ONE'4(12):'e8222.'doi:10.1371/journal.pone.0008222 http://www.plosone.org/article/info:doi/10.1371/journal.pone.0008222

Organization'of'ventral'pathway • Equally'responsive'to'all'features/objects? • No…seems'to'have'specialized'chunks'of' cortex'that'perform'somewhat'distinct' perceptual'functions • Often'referred'to'as'modules

26

‘Modules’'in'the'ventral'pathway'of'the'macaque'and'humans

Figure'4.18''(a)'Monkey'brain'showing'location'of'the'inferotemporal'cortex'(IT)'in'the'lower'part'of'the'temporal'lobe.'(b)'Human'brain' showing'location'of'the'fusiform'face'area'(FFA)'in'the'fusiform'gyrus,'which'is'located'under'the'temporal'lobe.

27

Functional'Module:'the'‘Fusiform Face'Area’'(FFA)'in'the'human'ventral'pathway

Area'responds'more'to'faces'than'to'other'objects

28

Size of response of a neuron in the monkey’s IT cortex that responds to face stimuli but not to nonface stimuli. (Based on data from Rolls & Tovee, 1995.)

Modularity: Structures for Faces, Places, and Bodies - continued

• Evidence from humans using fMRI: – Fusiform face area (FFA) responds best to faces. – Parahippocampal place area (PPA) responds best to spatial layout. – Extrastriate body area (EBA) responds best to pictures of full bodies and body parts.

Not'quite'so'simple… • Actually'not'just'a'single'‘module’ • Face'identity'likely'represented'by'distributed' code

Face'patches,'Doris'Tsao

Ethan M. Meyers, Mia Borzello, Winrich A. Freiwald and Doris Tsao, 2015, Journal of Neuroscience

All'patches'discriminate'individual' faces'and'objects'to'varying'degrees'

Ethan M. Meyers, Mia Borzello, Winrich A. Freiwald and Doris Tsao, 2015, Journal of Neuroscience

Hard'wired'organization? Or'Nature'vs.'Nurture??? • Are'functional'modules'like'the'FFA'hardwired'into'our'brains'via'evolution? • Or'are'they'shaped'by'experience? • Both?

36

37

Is brain activity in IT directly related to perceptual experience?

• Experiment by Sheinberg & Logothetis • Monkey was trained to pull two levers: one for a sunburst one for a butterfly • Binocular rivalry was used - each picture shown to one eye at the same time • Neuron in the IT cortex that responded only to the butterfly was monitored.

Figure 5-45 p116

Summary object recognition • Brain uses basic Gestalt grouping principles to organize input • Computational theories like RBC can help to explain how we build complex objects based on a simpler set of components (but not so good at fine details) • Neural activity in ventral visual cortex corresponds very closely to your subjective perceptual experience 40

Attentional control and dorsal visual pathway…

A simple card trick Pick a card, any card:

Attention

• William James (1890):

• “Everyone knows what attention is. It is the taking possession by the mind in clear and vivid form of one out of what seem several simultaneous objects or trains of thought. Focalization, concentration of consciousness are of its essence. It implies withdrawal from some things in order to deal effectively with others, and is a condition which has a real opposite in the confused, dazed, scatterbrain state…”

Attention

• William James (1890):

• “Everyone knows what attention is. It is the taking possession by the mind in clear and vivid form of one out of what seem several simultaneous objects or trains of thought. Focalization, concentration of consciousness are of its essence. It implies withdrawal from some things in order to deal effectively with others, and is a condition which has a real opposite in the confused, dazed, scatterbrain state…”

Attention

• William James (1890):

• “Everyone knows what attention is. It is the taking possession by the mind in clear and vivid form of one out of what seem several simultaneous objects or trains of thought. Focalization, concentration of consciousness are of its essence. It implies withdrawal from some things in order to deal effectively with others, and is a condition which has a real opposite in the confused, dazed, scatterbrain state…”

Where’s Waldo?

It implies withdrawal from some things in order to deal effectively with others

Where’s Waldo?

Selective attention • Attention can influence how fast you process information, and can influence how you search for relevant information (visual search tasks)…

• How does attention modulate perceptual representations— that is, what are the effects of attention on early sensory neurons in visual cortex?

Some targets of attentional modulation – regions that process information about specific visual features and objects! hMT+ (motion) V1-V4 (early vision) Superior temporal gyrus (early audition)

Fusiform gyrus (faces/houses)

V4 receptive field

Instructional fixation pt

Attention out of rf

Attention into rf

Eye movement to red

Motter (1994). J. Neuroscience, 14, 2190-2199.

Attention increases the firing rate of cells that respond to the attended location Switch attention into RF

V4 Switch attention out of RF

Motter (1994). J. Neuroscience, 14, 2190-2199.

Same general gain increase observed when you attend to other relevant features (motion, orientation, etc) or specific objects! Like making the object physically brighter!

Some sources of attentional control

Frontal eye fields (FEF)

Superior parietal lobule (SPL) and precuneus Intraparietal sulcus (IPS)

•

Disorder in which individuals are unaware of events in the space opposite to their lesion – Can be just vision, but most often includes other sensory or motor deficits

•

Importantly – Cannot be attributed to the sensory systems themselves – Ex. Individuals have normal vision in that region of space

•

Neglect is generally regarded as selective lack of attention

Visual Neglect

e would you live in?

Marshall and Halligan (1988, Nature)

Neglect •

Patients with neglect seem to live in a subjective world that is skewed away from the left side – may eat food from only the right side of their plate – ignore people who approach from their left – miss words on the left of the page when reading

•

Practically ignore all sounds and sights coming from their left side

•

May neglect parts of one’s own body – leave left side of face unshaven or without makeup – dress only right side of body – not acknowledge ownership of left sided limbs

•

Tend to behave as if nothing of importance is expected to be happening in the neglected space – Refrain from moving their left side or accept that they have a left side at all – May have a profound hatred towards the left side, and even physically abuse the left side

Drawings

Writing •

Patient is asked to write anything that comes to mind on regular lined paper

Neglect •

Neglect occurs in 11.0% - 37.8% of patients following brain damage

•

Characteristic lesion involves the right inferior parietal lobe/superior temporal gyrus – May include other lesion sites • Left TPJ • Supramarginal or angular gyrus • Inferior and middle frontal gyri

•

Subcortical Lesions – Thalamus – Basal Ganglia – Midbrain

Extinction •

Patients often recover from neglect after acute injury – Over a period of weeks of months

•

But may be left with long-lasting, milder version – “Extinction” – Failure to detect a stimulus contralateral to a lesion during simultaneous bilateral stimulation

•

Competition – Individuals will respond to a single event on the contralateral side – But they fail when a stimulus is presented simultaneously on the “good” side

Simultagnosia (Balint’s) • Complete inability to attend to more than one feature, regardless of the side of presentation – Even in fovea

• When presented with two spatially conjoint objects (ex. pen crossing over a pencil) – Will report only one – May report the other in other trials, but only one per trial

• Bilateral damage to parietal lobes

Conclusions • Attention modulates the response of neurons in visual cortex (increases their response) • Subregions of parietal cortex play a key role in attentional control (different aspects of control) • Failures of attention can be dissociated from failures of perception 87...