PSGY1010 Cognitive Psychology 1 Perception 1 PDF

PSGY1010 Cognitive Psychology 1 Perception I: Sensation and Perception Dr Chung Kai Li [email protected]  ▪ Further reading: Goldstein Wolfe, Kluender, & Levi Perception lectures ▪ Lecture 1: Sensation a...

PSGY1010 Cognitive Psychology 1 Perception I: Sensation and Perception Dr Chung Kai Li [email protected]  ▪ Further reading: Goldstein Wolfe, Kluender, & Levi Perception lectures ▪ Lecture 1: Sensation and Perception ▪ Lecture 2: Brightness and Colour ▪ Lecture 3: Depth and Visual Snowden, Thompson, & Troscianko Scene Analysis ▪ Lecture 4: Loudness and Pitch ▪ Lecture 5: Localisation and Auditory Scene Analysis  Today’s lecture Learning objectives: ▪ Describe the perceptual process ▪ Identify a range of situations in which perception departs from reality ▪ Distinguish between top-down and bottom-up processing ▪ Describe the modern scientific approach to studying perception 3  What is perception? ▪ Perception is generally defined as the process of acquiring knowledge about environmental objects or events via the senses ▪ The perceptual process is often broken down into two stages: ▪ Sensation is the process of transforming physical stimuli to electrical signals ▪ Perception is the process of interpreting these signals for conscious awareness and for action 4 The perceptual process Perception: signal processing and interpretation Sensation: conversion to Proximal Distal stimuli neural signals stimuli which are sent to 5 the brain  Evolutionary utility - what is perception for? ▪ Aristotle (384-322 BC): animals must have perception if they are to live ▪ Perception has evolved to aid the survival Somatosensory perception and reproduction of organisms (touch) ▪ All of our senses help us to seek out desirable objects Olfactory Visual and situations and avoid perception perception dangerous ones (smell) (seeing) Auditory Gustatory Humans: 5 senses perception perception or more? (hearing) (taste) 6 Also: Proprioception (sense of body position & movement), Nociception (pain), Thermoception (temperature)  Evolutionary utility - what is perception for? ▪ Importance of different types of energy in the environment determines which senses have evolved ▪ Some species sense energies that humans cannot: Caribou can sense light into Elephants are sensitive to very Snakes can detect infrared the UV spectrum, enabling low frequency sounds and radiation, enabling them to them to detect camouflaged vibrations, allowing them to generate a ‘thermal image’ predators communicate over large of prey distances 7  Is perception veridical? ▪ Senses would not evolve if they did not provide reasonably accurate information about the world ▪ However, this is not to say that perception is necessarily a clear window onto reality The eye has some similarities to a camera However, the eye does not transmit a picture – information about the pattern of light reaching the eyes must be interpreted by the brain. “What is real?”. Morpheus’ answer to Neo in The Matrix, 1999. 8  Illusions ▪ Loosely defined, illusions are situations in which perception differs from reality ▪ Let’s look at examples of two illusions in which we perceive objects at locations where no visual stimulus exists The ‘Lilac chaser’ ▪ Keep your eyes fixed on the cross. ▪ Throughout the movie there are always 11 pink blobs and one gap. ▪ What do you perceive? 9  Illusions The Hermann grid illusion ▪ Notice the illusory grey spots at the intersections of the white lines. ▪ Illusions can provide insight into the processes of sensation and perception 10  More illusions ▪ In some illusions, our perception of objects is systematically distorted Müller Lyer illusion Ponzo illusion which horizontal line is longer? which horizontal line is longer? Zöllner illusion Ebbinghaus illusion (Titchner circles) are the long lines parallel? which central circle is larger? 11 More illusions Café Wall illusion Shepard’s table illusion are the horizontal lines parallel? are the tables the same size? 12  Ambiguous figures ▪ Ambiguous figures are images that can give rise to two or more distinct perceptions The ‘Necker cube’ ▪ Note, our perception is rarely ambiguous, but tends to alternate over time or ▪ These figures are sometimes also referred to as bistable images 13 Ambiguous figures Old Lady Young/Old Lady Young Lady 14 Ambiguous figures Rubin’s vase Jastow’s duck/rabbit 15  Ambiguous figures ▪ Ambiguous figures sometimes produce #thedress different perceptions between different people that are stable over time 16  Ambiguous sounds ▪ Ambiguous sounds can also give rise to multiple bistable and stable perceptions Auditory stream ▪ Most people switch between hearing the sound segregation on the right as triplets of an A-B-A pattern or as two streams of A-A-A pattern and B-B-B pattern ▪ Laurel or Yannie? or Original High- Low- version frequency frequency shifted shifted 17  Impossible objects ▪ Sometimes sensory input is interpreted by the brain as representing objects or scenarios that are physically impossible Penrose triangle Schuster’s conundrum Endless stairs (Devil’s fork) Shepard scale Rissett rhythm illusion 18  Perception as interpretation Knowledge ▪ These illusions illustrate that perception is not a clear window onto reality Top-down ▪ Objects are not perceived directly Perception ▪ The brain is doing its best to figure out what is out there based on the available or Bottom-up information Sensory ▪ Two sources of information are available - input current sensory input and existing knowledge about the environment 19  Top-down and bottom-up processes Top-down ▪ use knowledge about the structure of the world to influence perception (sometimes referred to a ‘conceptually driven’ processes) Bottom-up ▪ take information from the senses and make judgements about the nature of the world solely based on this information (sometimes referred to as ‘data- driven’ processes) ▪ Both types of process are important - perception is frequently modified by knowledge, but knowledge can’t always override perception ▪ Historically, some theories of perception emphasise one component more than the other 20  Constructivist theories of perception ▪ Emphasise the importance of top-down processing ▪ Helmholtz (1821-1894) argued that the inadequate information provided by the senses is augmented by unconscious inference ▪ But Ibn al-Haytham (aka Alhazan) (c. 965-1040) is claimed to have had similar ideas much earlier… 21  Constructivist theories of perception ▪ Helmholtz (1821-1894) argued that the inadequate information provided by the senses is augmented by unconscious inference ▪ Details of the image are unconsciously completed ▪ This constructivist approach (see also Bruner, Neisser, Gregory) has a number of assumptions ▪ Perception is an active and constructive process ▪ Perception is an end-product of the presented stimulus and internal factors (e.g., hypotheses, expectations, motivations) ▪ It is prone to error 22  Constructivist theories of perception ▪ Gregory (1923-2010) elaborated the theory of perception as inference: ▪ “Perception is not determined simply by stimulus patterns; rather it is a dynamic searching for the best interpretation of the available data… perception involves going beyond the immediately given evidence of the senses” (Gregory, 1966) 23  Constructivist theories ▪ According to this approach, many illusions are better described as rational inferences rather than ‘perceptual errors’ Ponzo illusion Size constancy Hollow mask illusion The most common occurrence of converging lines In the real world faces are almost real 3D world is perspective distortion of parallel always convex, so our brains are lines. The brain tries to estimate the true properties reluctant to interpret face images of objects, so objects assumed to be further away as convex (even if they are) are perceived as longer/larger 24  Direct theories of perception ▪ Emphasise the importance of bottom-up processing ▪ James Gibson (1904-1974) argued that the constructivist approach may underestimate the richness of the sensory evidence we receive ▪ There are a great variety of cues in the natural world that provide much information about the structure of the environment ▪ The perceiver is not a passive observer but interacts with the environment – this interaction is also the key to picking up useful information 25  The modern approach – information processing paradigm ▪ Since the 1950s and 60s, perception has typically been approached as a computational process ▪ Focus on understanding the acquisition, processing, storage and recall of data in the brain Physiology Stimuli (neural Perception (sensory representations & & action input) processes) (output) 26  Key scientific approaches ▪ Modern approaches to studying perception probe the perceptual process in different ways Psychophysiology & brain Psychophysics Neurophysiology imaging / stimulation Stimuli Physiology Perception Stimuli Physiology Perception Stimuli Physiology Perception & action & action & action Measure relationship Measure the Measure the relationship between stimulus and relationship between a between physiological perception stimulus and the responses and physiological perception response 27  Summary Learning objective: Describe the perceptual process ▪ When thinking about the perceptual process, it can be useful to distinguish between two separate stages: ▪ Sensation ▪ Energy from physical stimuli in the environment stimulates sensory receptors ▪ Converted to neural impulses, which are sent to the brain ▪ Perception ▪ The brain processes and interprets this input 28  Summary Learning objective: Identify situations in which perception departs from reality ▪ Most of the time our perceptions are reasonably accurate, otherwise we would have difficulty navigating and interacting with the world ▪ However, our brain’s interpretation does not always coincide with the properties of the sensory input. Types of illusions include ▪ failure to perceive objects (e.g. Lilac chaser) ▪ perception of objects in the absence if a stimulus (e.g. Lilac chaser, Hermann grid) ▪ perceptual distortions (e.g. Müller-Lyer illusion) ▪ multiple perceptions of the same stimulus (e.g. Necker cube, Rubin’s vase) ▪ perceptions that are physically impossible (e.g. Penrose triangle) 29  Summary Learning objective: Distinguish between top-down and bottom-up processing ▪ Top-down ▪ use of context and prior knowledge in perception ▪ emphasised by constructivist theories (e.g. Helmholtz, Gregory) ▪ Bottom-up ▪ processing of sensory information as it is received ▪ emphasised by Gibson’s direct theory of perception 30  Summary Learning objective: Describe the modern scientific approach to studying perception ▪ The modern ‘information processing approach’ to perception focusses on the computational steps required to acquire, select, recall and process sensory information ▪ This is informed by complementary scientific approaches that probe relationships between sensory input, neural representations/processes and perception 31 Thank you Any questions?