Cognitive Lecture 2: Motion and perception


Gibson's Direct Perception

There is enough info in our environment to make sense of the world in a direct way - there is no need for processing/interpretation as the information we receive about size shape and distance etc. is detailed enough for us to interact with the environment (not a constructive process, bottom-up approach, all info already present) 

Perception = keeping in touch with environment and being able to cope with complex info arriving at the brain 

Classic theories argue: perception meaningless in itself, meaning is given by interpretation 

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Gibson's Ambient Array

Ambient array of light: optic array - all information from the environment which reaches the eyes (reflected angles of light from objects) 

Optic array is subjective - depends on position in environment but the information within is unambiguous or invariant and describes the layout of objects within the optic array, info comes in many forms 

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Visual information about the potential use of objects (Gibson 1979) - Objects affordance is directly perceived (intrinsic characteristic of the object, information that is immediately available in environment e.g. the objects HAVE affordances

Objects are perceived not only by visual features but also by potential motor actions 

Pappas and Mack (2008) - ppts see images of affordant objects under conditions in which they cannot be consciously perceived = brief mask exposure, prime stimulus briefly presented and masked by a target which calls for specific motor responses e.g. pressing a button based on visual stimuli. When response to a target corresponded with orientation of graspable part RT was faster 

Wilf et al (2003) - similar but considered general spatial compatibility confound normally present in studies looking at affordance effect e.g. the orientation of the graspable part creates an imbalance in the visual field (faster pressing left button b/c more info on left not b/c graspable) SO asked unrelated Q - action faster if object was graspable so affordance is perceived automatically

BUT - same object may have many affordances, what is automatically perceived?: based on learning, mood, and levels of creativity 

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Visually Guided Action

Visual information allows us to move within and interact with the environment - Gibson theories influence

Heading and steering: information which guides movements towards specific targets - without perception for visual info e.g. blind, intentional movement is compromised, important concept by Gibson is OPTIC FLOW (1950) 

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Optic Flow, Gibson (1950)

OF experienced when an observer moves towards an object or object moves = pattern of light reaches the eyes and changes at relative speed except the target which appears motionless e.g. airplane taking off/landing

Focus of expansion: specific point moving to/from - appears motionless 

OF and FoE allow movement towards a goal whilst avoiding obstacles 

FoE is invariant (higher order characteristic remaining unaltered as observers move around - important to direct movements (other invariants = texture gradients which converge to a point) 

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Optic Flow evidence

Smith et al (2006) showed dots patterns with different motion types and used fMRI to measure brain activity, V5 area: motion perception - medial superior temporal area particularly responsive to optic flow information, so MST involved in visually guided motion

OF doesn't make sense if we consider indirect movement towards an object (avoiding obstacles/curves) and when making a movement one usually moves head and eyes 

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Retinal flow field

RFF: changes in the pattern of light reaching the retina produced by observer moving in the environment as well as eye and head movements, made of linear retina flow containing a focus of expansion (= G's OF), and a rotary retinal flow produced by non-linear changes in the path/eye and head movements 

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Rotary Flow

Rotary flow disrupts linear flow pattern: how can we use information about heading from environment?

Snyder and Bischof (2010): 2 systems, 1 using motion (G's OF) and the other using retinal displacement (objects nearer direction of heading have less retinal displacement, those nearer observer have stronger retinal displacement = more informative), 2 systems more plausible e.g. 1 system using motion information quickly and automatically, second using displacement more slowly 

MST responsive to expansion and rotation and to a combination so this area may be able to compensate for distorted flow fields and decode information from retinal displacement to adjust visual flow perception 

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Curved Pathways

Some coherent retinal flow but not linear, where is the point of heading when moving along a curved pathway? 

Future-path strategy: observer identifies a number of points along a future path

Tangent point strategy: point on inside edge of the pathway at which direction appears to reverse 

Lippi et al (2013): drivers tend to switch from fixating a tangent point to fixating the path ahead as they negotiate curves (tangent point provides relatively precise info), drivers may use TP when uncertainty about the nature of the curve is maximal e.g. approach and enter, thereafter = future path 

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Time To Contact

TTC: information that allows us to predict the moment we will come into contact with objects 

Brain must have the ability to calculate the time in which the collision with an object may occur so we avoid accordingly. 

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General Tau, Lee (1976)

Observers do not need to work out speed or distance to approaching object, provided we approach at constant velocity we can use TAU: size of retinal image/rate of expansion, faster rate of expansion, less time to contact 

Tau-dot hypothesis: simple framework for explaining observers' time to contact but limited application - speed needs to be constant, time to contact with EYES not whole body, applied only to spherical symmetrical objects 

Need other cues: 

Hosking and Crassini (2010): object familiarity; binocular disparity (L/R differences in distance), stereoscopic vision (view with both eyes in similar ways), perception of depth, relative size (De Lucia, 2013), emotional value (Brendel et al, 2012) 

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Planning and control model

Glover: accounts for how people perform actions based on specific objects e.g. pen 

2 systems partially overlapping (planning and control) - both systems require visual information from the environment - planning intuitively begins before control but likely parallel, 2 separate systems related but controlled by different mechanisms 

Planning: activated before initiation of movement, identifies target, analyses affordances, decides how to grasp, works out timing of movement, metrical properties (Glover, 2004), influenced by TD and BU factors (goals, cog. load), relatively slow as it makes use of so much information and is influenced by cog. processes, requires the involvement of several areas (inferior parietal lobule), and planning and selection (PFC, MC, basal ganglia) 

Control: execution of a movement, ensures accurate movements and makes adjustments, efference copy - copy of efferent signal sent to muscles from primary motor cortex, used to compare actual and desired movements, proprioception: sensation of positions of ones body, visual perception = spatial characteristics of target, faster circuit than P and not susceptible to conscious influence, control depends on a visual representation located in superior parietal lobe and motor processes in cerebellum and basal ganglia 

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Glover (2012)

There are diff. types of actions, some more complex e.g. making a cake diff. than grasping an object.

G tested reaching and grasping actions in fMRI study - plan movement, plan then execute, execute movement immediately, observe target; contrast brain activation during one type of task with another

Planning involves: brain network in the medio-inferior parietal lobule, control involves: superior part of parietal lobule, supramarginale gyrus and cerebellum 

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TMS studies: involvement and causality

Glover et al (2005) TMS to superior parietal lobe as participants grasp size-changing object, control process disrupted by TMS to superior parietal lobe 

Streiemer et al (2011) applied TMS to ppts inferior/superior parietal lobe while they were planning to reach and touch a target, TMS disruption was greater when applied to inferior parietal lobe than superior 

Damage to inferior parietal lobe: ideomotor apraxia - poor at initiating movements in the direction of the target but can eventually control the action accurately 

Damage to superior and posterior parietal cortex: optic ataxia - difficulties making accurate movements to perform actions despite intact visual perception, system which corrects movement as an object moves doesn't work (Grea et al, 2002) 

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Perception of human motion

Johansson (1973): point-light sequence - people extremely perceptive to human motion - attached small points of light at joints and filmed movement in the dark, observers reported vivid impressions of human figurs even though there were a few isolated points, figure could be perceived 

Mather and Murdoch: participants can identify gender specific differences in movement e.g. walker, from displays due to a combination of physical factors, body structure and type of spatial arrangement. 

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Innate biological perception

Biological motion may be an evolutionary conserved and early emerging ability that serves as an ontogenetic (origination and development of an organism) and phylogenetic (evolutionary relationships) foundation for higher order social cognition 

Simion et al (2008): pointlight display of chickens to newborns, preferred to look at display showing biological motion than not, may be intrinsic capacity to perceive biological motion 

Pinto (2006): at 3 months perceptive to motion in point-light humans, cats and spiders, by 5 months, more interested in human motion (becoming more specialised) 

Cohen (2002): point-light display exp. sensitivity highest to human motion lowest to seal motion, more sensitive to observed motions resembling repetoire of actions 

Superior Temporal Sulcus: Thompson et al (2005): in fMRI STS strongly responds to moving bodies even through occlusion but not to disconnects moving parts 

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STS and motion detection

Gilaie-Dotan et al (2013): considered the effects of grey matter volume in the STS on motion detection, positive correlation with detection of bio motion but not non-bio (MRI, fMRI)

Virji-Babul et al (2013): human and object motion comparisons, brain activity very similar for first 200ms, then human activity associated with more activity in temporal lobe than object motion, NI = correlational evidence, activity in certain areas at certain times is associated with certain stimuli (EMG) 

Grossman et al (2005): applied repetitive transcranial magnetic stimulation (to the superior temporal sulcus) = temp. lesion, reducing sensitivity to bio. motion (TMS)

Saygin (2007): stroke patients with lesions in the superior temporal and premotor frontal areas that perception of biological motion was more impaired than non-biological motion 

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Biological motion specialty?

Communication tool: source of social and emotional information 

Interpretation tool: rely on visual info to interpret actions of others, e.g. movements of others eyes, infering body language, facial expressions 

Visually supported systems may be mediated by neural mechanisms specialized for the perception of bio. activity (STS) 

Atkinson (2004): observers ability to identify several emotions shown in point-light displays, high for fear, sadness and happiness 

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ASD deficits

Kanner et al (1943) autistic individuals exhibit chronic deficits in the ability to relate with others 

Baron-Cohen (1991) difficulties understanding the attitudes and intentions of other people 

Blake et al (2003): children with autism distinguishing bio from non-bio motion, tested children on perceptual grouping task involving perception of global form (performed worse for bio perception but not global perception 

Price et al (2012): asperger's individuals perform worse than controls for bio motion perception and motor skills tasks, poor motor skills and poor bio motion perception (others movements are special to us because they are part of our repetoire, can perform and perceive motion) 

Biological motion perception and theory of mind: ability to infer state of mine, intentions, desires, perspectives 

Rice et al (2016): link between ability to perceive bio motion and ToM in a sample of 7-12 year olds, strong relationship between performance in bio motion and 2 measures of ToM. 

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Mirror Neuron System

System underlying ability to detect humans mental state and intentions 

Rizzolatti and Gallese - EEG activity from neurones in monkey's brain when grasping, when the researcher picked up an object to hand to the monkey same neurones fired as when monkey grasped the object, mirror neuron that fired when a monkey grasped a peanut would only fire when researcher completed the same action 

Molenberghs et al (2012a): inferior parietal lobule, posterior inferior frontal gyrus, ventral premotor cortex, dorsal premotor cortex, superior parietal lobule, middle temporal gyrus, cerebellum 

Involved in working out reasons for the performance of an action: Umilta et al (2001) - visibly placing food behind screen, perform an action directed towards food either clearly or partially visible, MNS fired in both hidden and seen conditions, when there was no food, MNS didn't fire (meaning is important) 

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Iacoboni et al (2005)

MN to context sensitivity: certain actions mean different things according to context 

Intention condition - clips of 2 scenes involving a teapot, mug, biscuits, jar etc. showed objects being used e.g. drinking, and then after e.g. cleaning, hand shown grasping a cup in a different way for every scene 

Action condition - grasping actions shown as in intention but context was not shown - more activity in intention than action as the MNS may be involved in understanding intentions behind observed action 

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