W4 Sensation and Perception Notes

Week 4: Sensation and Perception

Learning Objectives

• Distinguish between sensation and perception.
• Discuss elements related to perception thresholds.
• Describe how systems create complex images in our visual system.
• Understand what sensation is.
• Identify our senses.
• Define perception.
• Determine thresholds for perception: absolute and difference.
• Explain how sensation and perception systems work together.
• Describe how we build complex images (with depth, distance, and movement) from simple visual information.

Types of Processing

• Bottom-Up Processing:
  • Starts with raw sensory input.
  • Begins with data from the senses and builds up to perception.
  • Example: Seeing a shape and realizing it's a cat based on features.
• Top-Down Processing:
  • Starts with prior knowledge, expectations, or context.
  • Uses existing knowledge to interpret what is sensed.
  • Example: Reading messy handwriting and still understanding it.

Sensation vs. Perception

• Sensation: Detecting stimuli and the world around us, converting them into neural signals our brain can understand.
• Perception: The active process of interpreting those signals based on expectations and surrounding context.
• Cognitive Psychology Approach: Emphasizes that perception is not a passive reception of sensory information but an active process of interpretation and prediction.
  • Perception actively involves interpreting and predicting what we experience.

Interaction of Sensation and Perception

• Sensation provides the raw data for perception.
• Sensory input is ambiguous.
• Perception actively works on sensory information.
• The brain uses predictive models to interpret sensation.
• Perceptual constancy: The ability to recognize objects despite different visual stimulation (lighting, orientation, viewpoint).

Brain's Predictive Models

• Little activation if you can predict a stimulus accurately.
• High predictability in self-produced stimuli (e.g., tickling).
• Good internal model for when we are speaking results in little activation of the auditory cortex because we can anticipate.
• Delayed feedback confuses our system (e.g., on the phone).
• Perception isn’t determined by the actual stimulus, but our prediction and interpretation of it.
• Disconnect between prediction and sensory input highlights how much our perception relies on internal forecasting.
• Frees up brain capacity and assists with distinguishing between own vs. other actions (e.g., schizophrenia).

What is Sensation?

• Ambiguous (refers to a situation, statement, or expression that has multiple possible meanings or is unclear due to a lack of specificity)
• Sensation: A stimulus-detection process where our sense organs respond to and translate environmental stimuli.
  • The process by which our sensory systems detect information from the outside world.
  • Needs to be translated into nerve impulses that are sent to the brain.
  • What you see with your eyes isn’t exactly the same data that your brain sees; it needs to be translated into something your brain understand.
• Factors that contribute to sensory judgments include:
  • Reward/costs for success or failure.
  • Significance of the stimuli.
  • Alertness and expectation.

What is Perception?

• Predictive (the brain gives it context on past experiences. The brain takes input and gives it meaning, based on context and existing knowledge)
• Perception is trying to make sense of what our senses are reporting.
  • Perception: Making ‘sense’ of what our senses tell us.
  • An active process of organizing and giving meaning to stimuli's input.
  • Interpretation and context are important.
  • In both incidents, although the stimulus is the same, your interpretation i.e. your perception is telling you is completely different
• The brain is constantly generating predictions about the environment around it.
• Does the model match that input, or not? Do we need to adapt it?
• The brain actively queries rather than just passively receiving information.
  • E.g., identifying birdsong.
• If a stimulus is predictable, the brain can work less, so there is less neural activity.
  • E.g., Tickle vs. Self-Tickle, as the brain predicted sensation.

Psychophysics

• Definition: The study of how physical stuff becomes our sensory experiences.
• Studies the relationship between the physical characteristics of stimuli and sensory capabilities (how we experience it).

Thresholds

• Absolute Threshold: Detecting something is there at all (e.g., the faintest, weakest thing).
• Different Threshold: The smallest change that we can notice.

More on Psychophysics

• Studies the relationships between the physical characteristics of stimuli and sensory capabilities.
• Evolutionary adaptability.
• Absolute limits of sensitivity.
• Differences between stimuli.

Absolute Threshold

• The bare minimum amount of physical energy needed for you to detect something.
  • The lower the threshold means the stronger the senses.
• This varies from person to person and can also depend on your mood; being tired raises your threshold because you are not as alert.
• The minimum amount of physical energy needed to notice a stimuli.
  • E.g., 50% hit rate in experimental conditions.
• Varies from person to person and situation to situation.
• Different species have evolved to process different types of information that are advantageous.
• Dogs' absolute threshold for smell is lower than ours, meaning they smell more.
• An eagle seeing a mouse from far up in the sky.
• Humans: How about your radiator warning light? Enough for you to see it but not enough for you to crash; lower thresholds indicate keener senses.
• For humans:

Difference Threshold

• Not about noticing every single time; it’s the point where you’re more likely to notice the point than not to.
• Someone turns up the TV – how long does it take before you notice the JND.
• Is the smallest difference between two stimuli that people can perceive 50% of the time.
• Detecting different stimuli can sometimes be just as important as the absolute threshold.
• Recognizing the pitch of your own childs cry.
• Recognizing spoiled food – Subtle changes make big differences.
• The difference threshold: the smallest difference between two stimuli that people can perceive 50% of the time.
  • Aka the “just noticeable difference”.
• Webers Law: Just noticeable difference is directly proportional to the magnitude of the stimulus (Weber Fraction) = tends to stay constant for all our senses.
  • A loud sound; it will take more for you to realize a noise change than when there’s a quiet sound.
• Actively involved in shaping our perceptions–alertness, expectation, and motivation.
• Alertness: If the stimuli is more important to you, it can affect how you perceive it.
  • Scary movie, and noises in house.
• Expectation: Not just about how long, it’s also a decision in a way. If you’re super alert youre way more likely to pick up on something, then when you’re relaxing.
  • Expecting phone call.
• Motivations: Reward vs. cost = if steaks are really high, you’re going to be way more tuned in = motivations matter too.

Subliminal Stimulation

• We might not see it consciously, but our brain still processes it, even if you’re not aware, and that can still activate feelings linked with what we saw/heard.
• E.g., smiling face, you might be more likely to say you’re happier at that point in time.
• People were scared about mind control and brain washing.
• Was not successful and not much evidence; you cannot be brain washed in subliminal messages.
• Happens a lot more with an upfront ad, then sneaking something into your subconscious.

Signal Detection Theory

• Many factors influence sensory judgements
  • Alertness, expectation, rewards/costs for success or failure, and the significance of the stimulus.
  • E.g., heightened sensitivity after a horror movie.
  • Perception is a decision, and it differs by person.

Subliminal Stimulation

• Stimulus is so weak or brief that, although it is received by senses, it cannot be perceived consciously.
  • Below our absolute threshold.
• Can be affected by this stimuli without being aware of it.
  • Subliminal stimuli (e.g., an image or word) can prime our responses to a later question.
• James Vicarys hoax led to the 1950’s fear of “mind control” and “brainwashing”.
  • Subliminal advertising outlawed.
• Persuasive stimuli above the perceptual threshold are more effective than so- called ‘subconscious manipulation’.
  • Effective only 5 minutes after primer and when thirsty.
• But there can be subtle effects on attitudes and judgments.

Human Senses

• Transduction: Conversion from one energy into another. Transduction coverts the characteristics of a stimulus into nerve impulses.
• E.g., vision: light energy (electromagnetic energy) is converted into nerve impulses.

Visual Processing

• Transduction: The sensory system for vision processes light energy.
• Transduction in vision involves changing electromagnetic energy (light waves) into nerve impulses.
• This occurs in the retina, which contains two types of photoreceptor cells:
  • Rods: black-and-white brightness receptors that function best in dim light.
  • Cones: color receptors concentrated in the fovea that function best in bright illumination.
• These receptor cells then synapse with bipolar cells, which in turn synapse with ganglion cells.
• Retinal Processing: The axons of the 1 million ganglion cells bundle up to form the optic nerve.
• The optic nerve then sends messages from the retina to a visual 'relay station' in the thalamus.
• Feature Detection: From the thalamus, the input is routed to the primary visual cortex in the occipital lobe.
  • Within the primary visual cortex are feature detectors, which are cells that fire selectively in response to visual stimuli with specific characteristics like edges, lines, and angles.
  • Different neurons are allocated for very specific shapes, and groups of these neurons can fire together to recognize more complex forms, potentially even unique celebrities.
  • For example, some neurons might fire for a line slanting right, others for a line slanting left, and others for a horizontal line; when these elements fire together, we might perceive the letter "A”.
• Parallel Processing: Brain cell teams in the visual cortex engage in parallel processing, where they process combined information about color, movement, form, and depth simultaneously.
• Recognition: Finally, the brain interprets the constructed image based on information from stored images, leading to recognition of what we see.
  • This involves analysis and reconstruction of the visual information that began with transduction.

Brain Parts and Processes in Vision

• Occipital nerve $\rightarrow$ Thalamus $\rightarrow$ Visual cortex (occipital lobe)

Our Senses

• Audition
  • Hear sound as pressure waves in the air.
• Olfaction
  • Chemical scents, rather than one of these energy senses like vision and audition.
• Gustation – taste
  • Chemical sense; olfaction and gustation can be argued to be one chemical sense.
• Touch (Tactician, sense of touch), Kinesthesis (motion) and Equilibrium (balance, vestibular sense).
  • Body senses.

Transduction

• The one thing these all have in common is that they do not speak the same language as our brain.
• Sensory systems are designed to extract the information we need to function and survive.
  • Vision processes light energy.
  • Hearing processes sound waves.
  • Transduction for vision uses electromagnetic energy otherwise simply known as light waves.
  • Transduction for hearing uses kinetic energy through mediums (like air or water), simply known as sound waves.
  • Transduction for taste uses chemical energy from food molecules into nerve impulses.
• Language of the environment = language of the brain
• Transduction converts the characteristics of a stimuli into nerve impulses.
• Sensory organs need to re-translate other forms of energy into one type that the brain can use.

Vision

• Stimulus is electromagnetic energy i.e. light waves
• Transduction changes this into nerve impulses
• Humans can see wavelengths 400 to 700 nanometres

Vision

Retina

• Retina consists of 120 mil. Rod-shapes and 6 mil. Cone-shaped light receptor cells
• Rods: black-and-white brightness receptors
  • -function best in dim light
• Cones: are our color receptors, and they're concentrated in the fovea
  • Function best in bright illumination
• Synapse with bipolar cells and then ganglion cells
  • We have 1 million ganglion cells who’s axons bundle up to form our optic nerve

After Transduction

• Analysis and reconstruction:
  • From the retina, the optic nerve sends messages to visual ‘relay station’ in the thalamus
  • Input is routed to the primary visual cortex in the occipital lobe
  • Then we have feature detectors: cells within the primary visual cortex fire selectively in response to visual stimuli that have specific characteristics

Feature Detectors

• Different neurons that are allocated for very specific shapes. For / \ – can fire together for “A”. Some neurons will fire when you see a line slanting towards the right or will fire when line slanting towards the left, the others will fire for a horizontal line. When those 3 fire together you might perceive it as the letter A
• Specific neurons can form circuits to correspond to unique celebrities

Sensation through Perception

• The scene
• Retinal processing: receptor rods and cones – bipolar cells and ganglion cells
• Feature detection: brains detector cells respond to specific features – edges, lines, and angles
• Parallel processing: brain cell teams process combined information about colour, movement form and depth
• Recognition: brain interprets the constructed image bases on information from stored images

Organisation and Structure

• Our brain actively organises incoming sensory information to create coherent perceptions, allowing us to make sense of what we see – Gestalt “The whole is more important than the sum of its parts”
• We perceive objects and scenes as organised wholes rather than just a collection of individual sensory elements.

Gestalt Perceptual Principles

• Figure ground relations:
  • Figure – the object that stands out (shape and structure).
  • Ground – the background, usually seen as shapeless and extending beyond figure.
• Similarity: We tend to group elements together that look similar to each other.
• Proximity
• Closure
• Continuity

Depth, Distance, and Motion

• Our retinas only perceive the world in 2D dimension; however, our perception allows us to experience a complex {3}D world. This is achieved though visual cues, Monocular and Binoculars.

Monocular

• Linear perspective
• Relative size
• Interposition (overlap)
• Texture gradient
• Light and shadow (create depth)
• Motion parallax

Binocular cues

• Binocular disparity (creates sense of depth) as both eyes get different views
• Convergence: inwards movement of our eyes when focusing on an object.

Gestalt

• Gestalt perception laws are the means by which we organise our sensations into coherent perception Organisation and structure:
• How do we organise our sensations into coherent perceptions? To make sense of what we see.
• Gestalt principles argue that the whole is more important than the sum of its parts
• Figure-ground relations are important in Gestalt i.e. the organisation of stimuli into a foreground figure and a background
  • Visual: a distinct shape on top of the scenery
  • Auditory: a melody is surrounded by chords/harmonies
• Gestalt perceptual laws
• Small circles form a triangle (similarity) 3 sets of 2 lines (paired them up with proximity)
• Incomplete circle (closure) See a-b as what goes over c-d (continuity) we see it as 2 lines crossing Gestalt perception laws can be tricked and used against you to misinterpret and misperceive a stimulus.
• The spiral is created by use, not the stimulus.

Depth, Distance and Movement

• Our retina perceives only {2}D, but perceptual constancy allows us to recognise familiar stimuli under varying conditions
  • Shape; brightness; size
• Depth cues:
  • Monocular: patterns of light/shadow, linear perspective (parallel lines converge, interposition, height on the horizontal plane, texture, clarity, relative size and the motion parallax (closer objects pass faster than distance)
  • Binocular: binocular disparity ({3}D movies use this ‘third finger’ phenomenon) and convergence (eyes move inwards)
• Modern psychology generally treats images on our retina, and therefore our mind, as {2}D
• Linear perspective, parallax, light and shadow and binocular disparity all allow us to see complex {3}D images through perception