PY1102 Sensation & Perception Lecture Slides PDF

PY1102 Exploring Psychology: from Perception to Reality Week 2: Sensation & Perception Dr. Sherry Aw Sensation and Perception Recap to last week Q – What is psychology? A – Psychology is the scientific study of mental processes and behaviour Q – If behaviour is the output, then what is the input?...

PY1102 Exploring Psychology: from Perception to Reality Week 2: Sensation & Perception Dr. Sherry Aw Sensation and Perception Recap to last week Q – What is psychology? A – Psychology is the scientific study of mental processes and behaviour Q – If behaviour is the output, then what is the input? A – Knowledge, memories, and... the outside world Most human behaviours are goal-directed, and the targets of these goals are things in the environment Like all animals, we have evolved systems that allow us to sense and respond to the outside world Source: Wikimedia Commons. Licensed under CC BY 2.0 Lecture Overview Part 1: Sensing and the Environment Part 2: Vision Part 3: Hearing Part 4: Other Senses Part 5: Perception Source: pixabay.com Licensed under CC BY 2.0 Part 1: Sensing and the Environment Sensation and Perception Sensation is the process by which the body gathers information about the environment and transmits the information to the brain for initial processing Perception is an active process by which the brain selects, organises and interprets sensory information Sensation and Perception An obvious but important point: psychological processes are enabled by a physical organ: the brain For the external world to influence the brain, we need systems and mechanisms that can convert physical stimuli into information that can be “understood” by the brain ◦ Electrical transmission ◦ Chemical transmission Five Basic Senses Different senses are sometimes referred to as sensory Vision modalities Five classical senses… but others too Somato- (e.g., proprioception) Audition sensation (Hearing) (Touch) Five Each modality has a mechanism for converting physical Main stimulus into signals Senses This process is known as transduction Gustation Olfaction Enabled by highly specialised cells known as sensory (Taste) (Smell) receptors Q – Why five main senses? Why not just one? What are the physical stimuli for the five senses? A – Different types of survival-relevant information What do all the senses have in common? a) Transduction b) Thresholds & Absolute Thresholds ◦ Just Noticeable Differences ◦ Signal Detection Theory c) Sensory Adaptation => All senses operate in the same way! They extract different information and process the information in different parts of the brain, utilizing specialized receptor cells Sensing the Environment - Transduction Transduction as the sensory process that converts information carried by physical stimulus (e.g., light) into neural messages (e.g., a change in membrane potential) ◦ Don’t panic! More on this in PY1101 (chapter 3 of this textbook) Sensory receptors are the site of transduction Eventually yields action potentials that travel to different brain regions These action potentials code for: ◦ Intensity of stimulus – no. firing neurons, firing rate (all or none) ◦ Quality of stimulus – types of receptors activated, different combinations Each system requires a minimum amount of energy to activate the system (threshold) Thresholds Sensory systems require a minimum amount of energy for activation (absolute threshold) Absolute Thresholds Average absolute thresholds across the five senses (Brown et al., 1962): ◦ Hearing – a watch ticking 6m away in a quiet place ◦ Smell – one drop of perfume in a large house ◦ Taste – one teaspoon of sugar dissolved in 10 litres of water ◦ Touch – the wing of a fly falling on your cheek from 1cm away ◦ Vision – the flame of a candle 50km away on a dark, clear night But… they vary between individuals! Q – How would these be established? Application: Hearing Tests Audiometry tests how well you can hear by establishing absolute thresholds https://www.youtube.com/watch?v=Sqdv-FUr9AI Difference Thresholds Difference threshold: the lowest level of stimulation required to sense that a change in stimulation has occurred Produced a Just Noticeable Difference (JND) Absolute threshold is actually a special case of the difference threshold 40 Degree Day 20 Degree Day – – 5 Degrees 5 Degrees Not Noticed Noticed Threshold Laws Important - there is no one-to-one correspondence between a stimulus and the resulting sensation One consequence of this is that JND is not always constant ◦ If your backpack is empty then adding an extra 2kg will feel noticeably different ◦ But, if you’re already struggling under a 30kg backpack, an extra 2kg won’t feel very different So… what are the rules that govern the JND? Source: pixabay.com. Licensed under CC BY 2.0 Threshold Laws Weber’s Law (1834): Regardless of the magnitude of two stimuli, the second must differ by a constant proportion from the first to be perceived as different ◦ i.e., the ratio of change required to produce a JND is constant This ratio differs between sensory modalities (and also between individuals, stimulus types) and is known as the Weber fraction JND is proportional to the intensity of the stimulus: ◦ JND is always large when stimulus intensity is high; small when stimulus intensity is low Threshold Laws Fechner’s Law: The magnitude of a stimulus grows logarithmically as the subjective experience of intensity grows arithmetically Went one step further than Weber, linking stimulus strength the intensity of the subjective experience Logarithmic function: ◦ at smaller magnitudes, increases yield a large increase in subjective intensity ◦ At larger magnitudes, increases yield smaller changes Source: Wikimedia Commons. Licensed under CC BY 2.0 Threshold Laws Fechner’s law holds up well in most situations, but not all ◦ e.g., the relationship between pain and stimulus intensity Steven’s Power Law: Subjective intensity increases in a linear fashion as actual intensity grows exponentially Can account for sensory modalities where larger Source: Wikimedia Commons. Licensed under CC BY 2.0 differences in subjective intensity occur at higher versus lower stimulus strengths Key message: sensation and stimulation are related, but not one-to-one Signal Detection Theory SDT goes one step beyond classical threshold theory Posits that sensation depends on characteristics of the stimulus, background stimulation, and the detector ◦ (e.g., response bias) How well you receive a stimulus depends on the presence of competing stimuli in the environment Explains why thresholds vary – not just between people, but within people Underscores the variability in human response and judgment Sensory Adaptation Sensory adaptation is the tendency of sensory systems to respond less to stimuli that continue without change ◦ e.g., walking into a bustling restaurant ◦ e.g., putting on a pair of glasses Happens in all sensory systems One way of filtering out irrelevant information so that more important information can be attended to Important exceptions: ◦ Visual system ◦ Intense pain Part 2: Vision Vision Probably the most important sensory modality in humans Enables remote sensing or exteroceptive perception We do not need to be in direct contact with a stimulus to sense and perceive it Q - Which other sensory modality allows for this? A - Audition Obvious evolutionary advantages to sensory abilities that Source: Wikimedia Commons. Licensed under CC BY 2.0 allow us to detect something before we are in direct contact with it The Nature of Light The visual stimulus is light Light is electromagnetic radiation falling within a specific range of wavelengths: roughly 400-700nm (the visible spectrum) Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th The brightness and colour of an object is determined by the wavelengths it reflects/absorbs Figure 4.4 The Eye Visual sense organ = the eye Collection, amplification, and filtering of visual stimuli Also contains the specialised photoreceptors necessary for transduction Photoreceptors located in the retina on the inner surface of the eye Transduction: Light → electrical signaling Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld The Eye – Blind Spot! The area where the optic nerve exits the eye is a blind spot – no photoreceptors on that spot. We are not actually blind because information from the left eye will compensate for the blind spot in the right eye, and vice versa. Find your blind spot! The Retina Contains two types of photoreceptors: “front” Rods (rhodopsin) Cones (photopsin) Action potentials Three sub-types of cone responding to produced here different wavelengths Short (blue) Medium (green) Long (red) Rods more sensitive than cones (low light vision) Cones concentrated in fovea Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th “back” Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld Receptive Fields Receptive field: the aspect of the external world that produces a change in firing rate of a given sensory cell Arises due to convergence ◦ Many rods → single ganglion ◦ Few cones → single ganglion Increasing convergence deeper into the visual system ◦ All visual system neurons after the ganglion cells have a receptive field Beginning of a process the enables construction of more advanced percepts Receptive Fields Many ganglion cells exhibit centre-surround organisation of their receptive fields Investigated using single-cell recording Two main kinds: ◦ On-centre, off-surround ◦ Off-centre, on-surround Allows detection of changes in stimulus between two parts of the receptive field Lateral inhibition Enables basic perceptual processes such as edge detection Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld Lateral Inhibition Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld Figure 4.10 Neural Pathways Left visual field → right hemisphere Right visual field → left hemisphere Topographic mapping approximately maintained in the visual system Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld Figure 4.11 The What and Where pathways The primary visual cortex (V1, striate cortex) contains feature detectors that arise through convergence and combination of receptive fields Simple cells – respond to lines of particular orientations in a particular region of space Complex cells – respond to lines of particular orientations, wherever they are in space Hypercomplex cells – respond only to lines of a certain length (they are “end-stopped”) The What and Where pathways From the primary visual cortex, visual information flows along two pathways (processing streams) The “What” pathway is involved in determining what an object is The “Where” pathway is involved in locating the object in space, following its movement and guiding movement towards it Much more on this in PY3109 and PY3110 Source: Cognitive Neuroscience, Fourth Edition Copyright © 2014 by W. W. Norton & Company, Inc. Perceiving in Colour Colour is a psychological property Three dimensions of colour: ◦ Hue is the apparent colour of an object (e.g., blue) ◦ Saturation is the purity of the colour ◦ Lightness is the extent to which a colour is light or dark Colour perception seems to be very similar across cultures But the number of labels for colours varies substantially across cultures Retinal Transduction of Colour Figure 4.13 Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld Theories of Colour Vision Young-Helmholtz (Trichromatic Theory): Colour is explained by differential activation of three colour receptors in the eye. ◦ Additive colour mixing ◦ Consistent with the anatomy of the retina ◦ BUT… cannot explain negative after images Opponent-Process Theory: Colours are derived from activity of three antagonistic systems: 1. Black-white 2. Red-green 3. Blue-yellow ◦ Can explain negative after images Likely that both theories hold true at different levels (retina versus higher centres) Negative Colour Afterimages Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th Figure 4.14 Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld Negative Colour Afterimages Part 3: Hearing The Nature of Sound Also known as audition Auditory stimulus = sound waves Sound waves = vibrations, variations in air pressure Is exteroceptive (like light) Requires a medium (unlike light) Human auditory range approximately 20Hz to 20,000Hz (20kHz) Outer ear directs and amplifies sound waves Figure 4.16 Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld ”Mosquito Tone” Our hearing range decreases with age Apparently, most people above the age of 25 will not be able to hear the sound of a mosquito buzzing. Try this out: https://www.audiocheck.net/audiotests_mosquito. php Figure 4.16 The Nature of Sound Frequency Amplitude Complexity Number of Height/depth of Combinations of cycles per the wave different second Measured in frequencies in a Measured in decibels (dB) given sound Hertz (Hz) Corresponds to Predominant Corresponds to the psychological pitch but with the psychological property of overtones property of pitch loudness or Corresponds to volume the psychological property of timbre The Ear Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld Figure 4.18 Transduction of Sound Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld Vibrations from the oval window causes pressure waves in the cochlear fluid These cause vibrations in the basilar membrane where the sensory receptors (hair cells) are located Mechanoreceptors bend, causing depolarisation and subsequent firing Figure 4.19 Neural Pathways Output from the cochlea is via the auditory nerve Decussation in the brainstem (cochlear and olivary nuclei) Subsequent projections to the inferior colliculus (midbrain), then the MGN of the thalamus Then to the primary auditory cortex (A1) Gross tonotopic mapping is maintained Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld Figure 4.21 Sound Localisation The visual system allows us to localise objects because of the representation of the visual field on the retina Q – How can we localise sounds? Two main cues used in sound localisation ◦ Difference in volume between the two ears ◦ Difference in timing between the two ears Binaural neurons, which respond to the difference in outputs from the two ears, enable localization Try this out! Virtual Barbershop: https://www.youtube.com/watch?v=IUDTlvagjJA Part 4: Other Senses Other senses In humans, vision and audition are the most highly specialised senses However, other senses still important for influencing the way we experience the world These are: ◦ Smell (olfaction) ◦ Taste (gustation) ◦ Touch (somatosensation) ◦ Further divided into pressure, temperature and pain ◦ Proprioception ◦ Further divided into position and movement Olfaction Olfaction: sense of smell Olfactory stimulus = odorants Molecules that enter nose either passively or during sniffing Transduction: assumed that odorants bind to specific chemoreceptors (although there is uncertainty)… …which opens ligand-gated ion channels and depolarises Chemoreceptors located in mucous membrane on roof of nasal cavity Send signals to the glomeruli in the olfactory bulb Transduction of Smell Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld Figure 4.22 Fun Fact! COVID-19 and Scented Candle Reviews https://www.washingtonpost.com/business/2020/12/01/covid-scented-candle-reviews/ Gustation Gustation: sense of taste Gustatory stimulus = tastants Chemical sense similar to olfaction Receptors located within taste buds, which are found in papillae of the tongue Transduction: tastants enter via taste pore and bind with receptors in taste cells …which (eventually) opens gated ion channels and depolarises – but sometimes molecular cascades involved Two pathways: ◦ → brainstem → thalamus → primary gustatory cortex (conscious identification) ◦ → brainstem → limbic system (immediate emotional and behavioural reactions) Transduction of Taste Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld Figure 4.23 Basic Taste There are five basic tastes Not mentioned in your textbook for Each has specific taste receptors some reason Salty Innate preferences for certain tastes (e.g., sweet vs. bitter) Umami Sour Basic Plus also nociceptors (pain) for different Tastes “irritants” ◦ e.g., capsaicin Sweet Bitter Complex combinations → complex tastes Babies Eating Lemons https://www.youtube.com/watch?v=0J0SbRPEC_w Somatosensation Somatosensation: sense of touch Also encompasses pain (nociception), location in space (proprioception), heat/cold (thermoception) Somatosensory stimulus varies! Different receptor classes: ◦ Mechanical Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld ◦ Thermal ◦ Polymodal Merkel’s disks (regular touch) Meissner’s corpuscles (light touch) Receptors located under skin and within Pacinian corpuscles (deep pressure) muscles/joints Krause’s end bulbs (temperature) Skin is the largest organ in our body! Ruffini endings (temperature) Somatosensation What about Tickling? Still a lot we don’t know about tickling – why do we laugh when we are tickled? Any evolutionary advantage to tickling? Thought to involve similar receptors as itching – ”free” nerve endings Other animals are also ticklish! Rats giggle at 50kHz, which is out of our auditory range Nociception Pain is a source of information that relates to tissue destruction Pain is adaptive to a degree (motivates behaviours to terminate the source of the pain). Pain is influenced by ◦ Cultural beliefs ◦ Emotional states (e.g., fear, stress etc.) ◦ Personality (e.g. neuroticism) Proprioception Register body position and movement Vestibular sense: provides information about the position of the body in space by sensing gravity and movement Kinesthesia: provides information about the movement and position of the limbs and other parts of the body relative to one another Part 5: Perception Perception Perception = organisation + interpretation (+ attention) Combines arrays of sensations into meaningful units. E.g.,: 1. Color: Green 2. Shape: Oblong 3. Feel: Sharp and Thorny 4. Smell: Pungent Perception In this section we concentrate on the visual system Four aspects of perceptual organisation are: ◦ Form perception ◦ Depth or distance perception ◦ Motion perception ◦ Perceptual constancy Form Perception Organisation of sensations into meaningful shapes and patterns Gestalt Principles Experiments in 1920s and 1930s established basic Figure-ground perception perceptual rules for interpretation of sensory Similarity information Proximity These basic perceptual rules are known as Gestalt Good continuation principles Simplicity Gestalt loosely translated to “whole” or “form” Closure Ambiguous Figures Source: Wikimedia Commons. Licensed under CC BY 2.0 Gestalt Principles Similarity Proximity Good Simplicity Closure Continuation Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld Figure-Ground Perception Source: Wikimedia Commons. Licensed under CC BY 2.0 Perceptual Illusions Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld Figure 4.30 Depth or Distance Perception The organisation of perception in three dimensions Retinal images are two dimensional Perceptual processes are required to construct the third dimension of depth Two kinds of visual information provide important information about depth and distance: Binocular cues: visual input integrated from the two eyes Monocular cues: visual input from one eye Source: pixabay.com. Licensed under CC BY 2.0 Depth Perception Cues Monocular Cues Binocular Cues Interposition: One object blocks another Retinal disparity: Eyes positioned slightly differently, receive slightly different images Linear perspective: Lines converge ◦ Leveraged for 3D movies/TV Texture gradient: Distant objects finer Convergence: Eyes become more “crossed” Shading: 3D objects cast shadows when focusing on objects that are closer Aerial Perspective: Far objects are fuzzy Motion-Related Familiar size: Familiar objects that appear small are Parallax: In motion, nearer objects move inferred to be distant across visual field faster Relative size: The smaller of two objects is seen as further away Motion Perception Visual system is wired to detect motion ◦ Rods in retina are sensitive to motion ◦ Happens through convergence on ganglia with very large receptive fields ◦ Concentrated in the periphery ◦ Neurons in visual cortex respond to motion ◦ More refined motion detection further up the “where” pathway Two systems for processing movement: ◦ A: eye is stationary as object moves → Changes in stimulation across retina produce perception of movement ◦ B: eye moves to maintain object at same place on the retina → muscle signals are used to infer movement  Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld Motion Perception Figure 4.33 Perceptual Constancy 1. Colour: Tendency to perceive object colour as stable, even under conditions of changing illumination 2. Shape: We recognise an object as having the same shape although we may view it from a different angle, at a different distance 3. Size: Objects do not differ in size when viewed from different distances The Influence of Experience The previous sections were mainly about the organisational aspect of perception Interpretation goes one step further ◦ e.g., object recognition Deeply intertwined with memory Key question – how much influence does memory and expectation have on our perceptions? It’s about how you weight the balance between top-down and bottom-up influence Nature versus nurture  Source: Burton, L., Westen, D., & Kowalski, R. (2015). Psychology: 4th Australian and New Zealand Edition (4th ed.). Wiley & Sons: Milton, Qld Top-Down and Bottom-Up Processing Figure 4.36 Summary Sensation (process whereby sense organs gather information about the environment) vs perception (process whereby the brain selects, organises and interprets sensation) Thresholds (absolute and just noticeable) refer to the minimum intensity (or change thereof) of a stimulus needed for detection to occur Perceptual organisation integrates sensations into meaningful information. It is influenced by experience