Foundations of Perception and Cognition Lecture Notes PDF

Foundations of Perception and Cognition Introduction to Sensation Perception Dr Deanne Green  We acknowledge and pay our respects to the Kaurna people, the traditional custodians whose ancestral lands we gather on. We acknowledge the deep feelings of attachment and relationship of the Kaur...

Foundations of Perception and Cognition Introduction to Sensation Perception Dr Deanne Green  We acknowledge and pay our respects to the Kaurna people, the traditional custodians whose ancestral lands we gather on. We acknowledge the deep feelings of attachment and relationship of the Kaurna people to country and we respect and value their past, present and ongoing connection to the land and cultural beliefs. Perception Lectures What will you learn 1. Intro to sensation and perception 2. Methods 3. Spatial vision 4. Body senses 5. Depth perception 6. Motion perception Warning !! We will be talking about animal experimentation in this lecture Warning Mathematical models for sensory measurement Part 1 Sensory processes Mathematical models Debate about representations for sensory measurement Mathematical models Classification of the senses Sense Sensation Receptor Sensory Cortex Structure Vision Electromagnetic Photoreceptors Eyes Primary Visual energy Cortex Hearing Air pressure Mechanoreceptors Ears Auditory Cortex waves Touch Tissue distortion Mechanoreceptors Skin, Muscle Somatosensory Thermoreceptors Cortex Taste/Smell Chemical Chemoreceptors Nose/Mouth Taste and Olfactory Cortex Balance Mechanoreceptors Vestibular Temporal Cortex organs Perception Awareness Stimuli Organism’s response Hierarchical stages of sensory processing Hierarchical stages of sensory processing Hierarchical processing of sensory information involves transmission of information to different areas The process in the lower levels control, modify, and modulate the process The result is stark perceptual errors (like the strawberries and dress from Monday) But there is debate: Ø Representations? Ø Computations?  Response to stimulus changes as a function of the intensity of the stimulus Stevens’ power law The relationship between the strength of a physical stimulus and the perceived magnitude increase i.e., the relationship between the sensation of the stimulus and the perception of the stimulus Linear scale Nonlinear scale Using deficiencies to measure sensation Part 2 Lesion experiments Clinical studies Using deficiencies to measure sensation Lesion experiments A section of an animal’s brain is lesioned (through surgery or ablation) Behaviour in the lesioned animal is then compared to an intact animal Lesion Example Ferrier (1876) removed the angular gyrus of monkeys Angular gyrus Lesion Example Ferrier (1876) removed the angular gyrus of monkeys The monkeys were no longer able to drink Ferrier concluded that the animals were now blind What do you think about that conclusion? Lesion Example Vision is processed largely in occipital cortex (not in the gyrus) Lesion Example Vision is processed largely in occipital cortex (not in the gyrus) The angular gyrus is responsible for attention, self-processing, semantic information processing, emotion regulation, and mental imagery. A complex region needed for visually guided action Ability to do visually guided action was damaged, not vision itself Pros and cons of Lesion Experiments Can remove specific regions The data helped establish the idea of localisation of function However, as our knowledge of the brain grew, we learned that discrete areas of brain function are rare. Clinical studies Patients with brain injury Ø Trauma (e.g. accident, war wounds) Ø Disease (e.g. Parkinson’s disease) Clinical studies Assess functional and anatomical extent of insult Ø Neuropsychological tests Ø Experiments Insight into brain function by comparing patient behaviour to behaviour of non- injured person Example: Patient DF Clinical Example Patient DF was a woman with visual apperceptive agnosia due to injury Bilateral (both sides) lesion to her lateral occipital cortex Clinical Example Patient DF was a woman with visual apperceptive agnosia due to injury Bilateral (both sides) lesion to her lateral occipital cortex Vision was intact – but couldn’t visually locate or identify objects.  Matching Posting Patient DF Control What ability did patient DF lose? Patient DF cannot judge the width of an object by using her thumb and forefinger However, when asked to pick it up, her hand moves to the correct width Her estimates do not improve thereafter, but she continues to accurately pick up the object Thus she cannot judge features of the object but is able to control her actions with that information What does this tell us? Grip aperture complicated motor adjustment? Difference in types of task, draw on different brain abilities? Maybe perceptual judgement is less complicated? The preserved visual control of grasping in is mediated by the intact visuomotor networks, whereas her failure to perceive the form of objects is a consequence of damage to her ventral stream Pros and Cons Very interesting cases Ø Lateralised occipital lobe damage: only able to see half of things Ø Prosopagnosia: unable to recognise faces including own! Ø Corpus Callosotomy No two patients the same Ø Age Ø Extent of injury Ø Experience prior to injury Using perception to measure sensation Part 3 Psychophysics Using perception to measure sensation Psychophysics Investigating the relationship between stimuli and the sensations and perceptions they produce. Psychophysical techniques Method of limits Ø Stimuli level is gradually increased until the participant reports that they are aware of it Method of constant stimuli Ø Presented in random levels and participants reports detection Method of adjustment Ø Participant controls the level of the stimulus until it is just barely detectable Pluses and minuses Non-invasive technique Relatively inexpensive Relies on participant judgment Behaviour is often what matters - useful information for applied areas (e.g. human factors, assessment of disease) Using neural function to measure sensation Part 4 Single Unit recordings Using perception to fMRI studies measure sensation Single unit recordings Record the change in action potential of a single cell (neuron) Record from awake, behaving or anaesthetized animals Physiology refresher Information about a stimulus is transmitted from one part of the brain to another via neurons Action potentials are the messages that neurons send each other Pros and Cons Excellent spatial and temporal resolution Only a very small window into brain activity Long, expensive experiments Functional Magnetic Resonance Imaging (fMRI) Measures change in blood flow Shows brain activity Has been used to infer localisation of function E.g., showing patient DF images in the fMRI and seeing if the occipital lobe lights up Comparing temporal, special and resolution of different techniques fMRI for Dummies fMRI set up schematic With thanks to Culham Lab Slice Terminology VOXEL Slice Thickness (Volumetric Pixel) e.g., 6 mm In-plane resolution e.g., 192 mm / 64 = 3 mm 3 mm 6 mm SAGITTAL SLICE IN-PLANE SLICE 3 mm Number of Slices e.g., 10 Matrix Size e.g., 64 x 64 Field of View (FOV) e.g., 19.2 cm Soares et al, 2016 Cortical Surfaces segment gray-white render cortical surface inflate cortical surface matter boundary sulci = concave = dark gray gyri = convex = light gray Culham Lab Cortical surfaces render cortical surface inflate cortical surface sulci = concave = dark gray gyri = convex = light gray segment gray-white matter boundary With thanks to Culham Lab Category Specific Visual Areas objects faces places With thanks to Culham Lab Pros and cons Whole brain activity in real time (i.e. as experiment is performed) Not fantastic temporal and spatial resolution Very expensive, time consuming experiments Summary Reference Barlow, H (1972): Single units and sensation: A neuron doctrine for perceptual psychology. Perception 1:371-394. Mather, G (2016): Foundations of perception Psychology Press Ltd., Hove Chapter 1