Sensation and perception researchers cover a range of specialties: ophthalmology, audiology, neuroscience, etc.

Understanding sensation and perception means being able to comprehend the physical properties of objects of our perception.

From a psychology perspective: understanding the physical structures and functions of the sense organs + brain’s conversion of sensory information into perceptual experience.

Perception is the brain’s best guess at what is occurring in the world based on the given sensory signals. Perceptual illusions showcase that these guesses from perception may not necessarily reflect reality.

What are the processes and purposes of sensation and perception?

• We do not experience stimuli directly.

  • Senses relay information abt stimuli for us to process later on and form a perception of our surroundings

• Sensation: receive energy from stimuli, convert to action potential

Sensory systems:

• Have specialized receptor cells, transduction, multiple subsystems

  • Each sense organ has specialized receptor cells that help us detect physical energy

Process of sensation:

• Cells register stimulus

• Transduction occurs (energy converted to action potential)

• When reaches brain, information travels to appropriate part of the cerebral cortex

Perception gives meaning to sensations. We organise and interpret sensory info so it makes sense

Remember!!!

• Sensation: raw materials of experience inputted

• Perception: the brain’s best interpretation of sensory input

What are Bottom-Up and Top-Down Processing?

Bottom-Up processing (first time reacting):

• Senses receive information abt environment then send up to brain for processing

• Take in information (sensing), and making sense out of it (perception)

Top-down processing (already have expectation):

• starts with cognitive processing in the brain (prior knowledge)

• apply results of processing to incoming stimulus

both processes work in tandem to allow us to function accurately and efficiently

What good is perception?

• Improve chances for survival (sense and respond quickly and accurately to stimuli)

• Each species is adapted to the habitat in which it evolved

  • Predators = eyes at front of face to perceive prey accurately

  • Preys = eyes on sides of head, giving wide view of surroundings

How are sensory receptors and the brain connected?

• Sensory receptors (detect stimulus, convert to action potentials) → transmit thru sensory/afferent nerves → brain

  • Types of energy receptions:

    • Eyes : photoreception

    • Hearing : mechanoreception (detects vibrations)

    • Touch : mechanoreception (detects pressure as touch)

    • Smell : chemoreception (detects chemical stimuli, perceive as smell)

    • Taste : chemoreception (detects chemical stimuli, perceive as taste)

How do sensory receptors vary based on intensity of stimuli?

• Sensory neurons follow all-or-nothing principle. Since the intensity of the stimulus cannot be communicated by changing the strength of the action potential, the receptor varies the frequency of sending an action potential.

Cases of “confusing” senses:

• Synaesthesia: one sense induces an experience in another sense (being able to “see” music)

• Phantom limb pain: after amputation, areas of brain which receive information from those receptors are still there and cause confusion

What happens when the information from sensory nerves are sent to the brain?

• Sensory signals tend to immediately go to the thalamus (the relay station of the brain)

• Signals are routed to specific sensory areas of the cerebral cortex (specialised to handle different sensory functions):

  • Visual: occipital

  • Hearing: temporal

  • Pain, touch, temperature: parietal lobes

What are the thresholds for detecting stimuli?

How much of a stimulus is necessary for you to see, hear, taste, smell, or feel something?????

What is the absolute threshold?

The point at which an individual detects stimulus 50% of the time

What is the difference threshold?

The difference which must exist between two stimuli before the difference is detected.

• Weber’s law: two stimuli must differ by a constant proportion to be perceived as different (maksudnya, theres like a specific ratio, or percentage difference that needs to be fulfilled in order for a difference to be detected)

Is subliminal perception possible?

• Detection of info below level of conscious awareness.

• Can behaviour be influenced by stimuli presented so quickly/at a weak level to the point we can’t perceive them?

• Yes, it’s possible and can influence behaviour (still weak influence tho)

What is signal detection theory?

• Focuses on decision making about stimuli under conditions of uncertainty

• Detection of stimuli doesn’t just rely on physical intensity of stimulus and observer’s sensory abilities, but also other variations such as fatigue, expectations and the urgency of the moment.

Four Outcomes in Signal Detection:

Imagine you’re out somewhere and you see someone attractive. You look for indications to make a decision on whether to ask the person out or not.

• Signal present: the person would say yes

• Signal absent: person would say no

• “Yes, I see the signal” : you notice the person would’ve said yes and you ask them out

• “No, I don’t see the signal” : you don’t ask the person out

1. Hit:

   1. Signal present and “Yes, I see the signal”

   2. Person says yes and you ask them out

2. Miss

   1. Signal present and “No, I don’t see the signal”

   2. You don’t ask them out but they would’ve said yes

3. False alarm

   1. Signal absent and “Yes, I don’t see the signal”

   2. You ask them out, but they reject you

4. Correct rejection

   1. Signal absent and “No, I don’t see the signal”

   2. You don’t ask them out and they would’ve rejected you

Components for decision making in signal detection theory:

• Information acquisition: gathering relevant indicators (does the person have a wedding ring? is the person walking with a significant other? are they attractive)

• Criterion: standards to make a decision (whats the worst outcome? whats the opportunity cost of asking this person out? LMAOOAOOAOAOA)

What does signal detection theory tell us?

• Examine processes that underlie our judgements about whether we perceive a stimulus or not

  • Tested by varying intensities, or asking participants to report on their detection of the sound or sight of interest

• Consider mistakes a perceiver might make and the reasons behind such errors

What factors influence our perception?

• Attention

  • Focusing awareness on a narrow aspect of the environment

• Selective attention

  • Focusing on a specific aspect of experience while ignoring others

The Stroop effect:

• Automatically reading the name of a colour can make it difficult to name the colour of ink that the word is printed in

• Automatic perception of word makes reading easier, but makes it harder to ignore the colour of the words

What features of stimuli draw our attention?

• Novel stimuli: new, different, unusual

• Size, colour, movement

• Emotional stimuli

  • We are more quicker to identify an emotional stimulus than a neutral stimulus

  • Downside: emotion-induced blindness

    • When we encounter an emotionally charged stimulus, we fail to recognise a stimulus presented immediately after it.

    • E.g. you see an ambulance, but you don’t notice the cars around you or road signs bc youre preoccupied by the ambulance

• Inattentional blindness:

  • Attention is occupied, that you fail to detect unexpected events (even interesting ones)

  • Remember: ball-throwing gorilla video

How does perceptual set influence perception?

• Perceptual set: readiness to perceive something in a particular way

What is sensory adaptation?

• a change in the responsiveness of the sensory system to the average-level of stimulation

What is the Visual System?

• Ability to detect visual stimuli depends on sensitivity of our eyes to differences in light

What is light?

• Electromagnetic energy

• We can only see in the visible light spectrum

• Wavelength: determines the light’s hue or colour

• Amplitude: the brightness of the stimulus

• Purity: perceived saturation of a visual stimulus

The structure of the eye:

• Sclera: white, outer part that maintains the shape of the eye and protect it from injury

• Iris: coloured part of the eye, contains muscles that control the size of the pupil and the amount of light that gets into the eye

• Pupil: centre of iris, an opening

• Cornea: clear membrane just in front of the eye. Bends light to focus it at the back.

• Lens: transparent and somewhat flexible disk-like structure filled with a gelatinous material. Bends light to focus it at the back.

Myopia (near-sightedness): lens and cornea loses ability to focus faraway objects correctly onto the back of the eye.

• Retina: at the back of the eye, light-sensitive surface that records electromagnetic energy and converts it into neural impulses for processing in the brain. Is the primary mechanism of sight.

  • Contains 126 million receptor cells

    • Rods (120 million): most sensitive to light, but not useful for colour vision, don’t allow us to see fine detail. —> work well under low illumination (most active at night)

    • Cones (6 million): responsible for colour perception and seeing small details

      • Require more light to respond than rods do (operate best in daylight or high illumination)

• Fovea: contains only cones.

  • But cones can also be scattered outside of the fovea

How does the brain process visual information?

• Stimuli in the left visual field stimulate rods and cones in the right half of the retina in both eyes (and vice versa)

• Optic chiasm (point in the brain): optic nerve fibres separate and approximately half of the nerve fibres cross over the midline of the brain

Objects in left visual field:

• Stimulate right half of the retina in both eyes

• Transmitted to right side of the occipital lobe in the cerebral cortex

Objects in right visual field:

• Stimulate left half of the retina in both eyes

• Transmitted to the left side of the occipital lobe.

What does the visual cortex do?

• Located in occipital lobe at the back of the brain is involved in vision

• Most visual information goes here before it moves to other visual areas to be processed for further analysis.

• Cells are highly specialized.

  • Feature detectors: individual neurons/group of neurons in the brain’s visual system that respond to particular features of a stimulus.

  • Visual cortex has neurons that are individually sensitive to different types of lines, angles, or movement in a particular direction.

There is a critical period in visual development in which the brain requires stimulation to develop certain capacities —> learns to perceive through experience

How is visual information processed so fast?

• Parallel processing: simultaneous distribution and management of information across different neural pathways

  • Perceive “what” and “where” all at once

How do we integrate all the visual information?

• Binding: bringing together and integration of what is processed by different pathways or cells.

  • Combine information you’re seeing to form a complete image in your cerebral cortex

How do we see colour?

• Trichromatic theory (Young and Helmholtz):

  • Colour perception produced by three types of cones sensitive to different but overlapping range of wavelengths

  • Visual system bases its perception of colour on the relative responses of three receptor systems: cones sensitive to red, blue and green

  • Colourblindness supported by this theory

    • Depends on which of the three kinds of cones is not working

• Opponent-process theory (Ewald Hering):

  • Some colours cannot exist together, whereas others can (e.g. greenish blue vs reddish green)

  • Trichromatic theory could not explain afterimages.

  • Cells in visual system respond to red-green and blue-yellow colours; a given cell might be excited by red and inhibited by green, whereas another cell might be excited by yellow and inhibited by blue.

    • Stare at red too much, ‘red-green’ system seems to ‘tire’ and when you look away it gives a green afterimage

Which is correct? Both are correct.

Why?

Red, blue and green cones in retina are connected to retinal ganglion cells in such a way that three-colour code is translated into opponent-process code

How do we perceive shape, depth, motion and constancy?

• How do we see shape?

  • What we see by contours (locations at which a sudden change of brightness occurs)

  • Figure-ground relationship:

    • Organise stimuli into figures and background.

Gestalt psychology: how people naturally organize their perceptions according to certain patterns —> main principles: “the whole is more than the sum of its parts”

• Closure: when we see something disconnected, we fill in the spaces and view them as complete figures

• Proximity: when objects near to each other, seen as a unit

• Similarity: objects similar to each other, seen as a unit.

How do we see depth and distance?

• Depth perception: perceive objects 3d and perceive distance from you

  • Binocular cues: depth cues that derive images from the left and right eyes and on the way the two eyes work together

    • The disparity between the images determine depth. (the more different, the closer)

    • Convergence: our eyes are focused on the same object. If object is near, pupils converge. If object is far, we can focus without pulling eyes together. The more cross-eyed you have to be, the closer the object is.

  • Monocular cues: provide information about depth and distance, but require only one eye to assist us.

    • Familiar size: what we’ve learned from experience about the standard sizes of objects

    • Height: objects positioned higher look like they are farther away

    • Linear perspective: parallel lines appear to converge with distance. As sides get closer together, they are farther away from you.

    • Overlap: object partially conceals or overlaps another object closer to you

    • Shading: position of light and the position of viewer. Tells us about the shape of the object.

How do we see motion?

• Neurons specialised to detect motion

• Feedback from body tells us whether we are moving or something else is moving (from movement of eye muscles)

• Environment is rich in cues that give us information about movement

How do we recognize objects when the sensory input changes?

• Perceptual constancy: recognise that objects are constant and unchanging even though sensory input about them is changing

  • Size constancy: same size even though retinal image of object changes (no matter how far you are from your car, you perceive your car as a constant size)

  • Shape constancy: object retains the shape even though its orientation to you changes (no matter which angle you look at your car from, it still has the same shape)

  • Colour constancy: even with different amounts of light, the object still retains the same colour (car still has the same colour no matter what amount of light it is under)

What is the auditory system?

Sound waves are vibrations in the air processed by auditory (hearing) system.

• Wavelength: wave’s frequency

  • Pitch: interpretation of the frequency of a sound

• Amplitude: measured in dB is the amount of pressure the sound wave produces

  • Volume

• Timbre: tone saturation or perceptual quality of a sound

What are the structures and functions of the ear?

• Outer Ear

  • Pinna: funnels sound into the interior

  • External auditory canal

• Middle Ear

  • Eardrum: vibrates in response to sound

  • Hammer

  • Anvil

  • Stirrup

    • Muscles that operate the bones take eardrum vibration and The bones vibrate to transmit sound waves to the fluid-filled inner ear.

• Inner Ear: convert sound waves into neural impulses and send to brain

  • Oval window

    • Stirrup connected here —> transmits sound waves to cochlea

  • Cochlea: fluid-filled structure coiled up like a snail’s shell

    • vibrations from stirrup causes the fluid in the cochlea to vibrate

    • vibrations move along portions of basilar membrane

  • Basilar membrane:

    • lines inner wall of cochlea and runs its entire length

    • narrow and rigid at base of cochlea but widens and becomes more flexible at the top

      • flexibility allows diff areas of basilar membrane to vibrate more intensely when exposed to different sound frequencies.

    • lined by hair cells (sensory receptors)

      • the movement of these hair cells against the tectorial membrane generates action potentials that the brain interprets as sound

what theories explain hearing?

• place theory

  • each frequency produces vibrations at a particular spot on the basilar membrane

  • experiment: effects of vibrations on oval window on the basilar membrane of human cadavers

    • stimulation produced travelling wave on basilar membrane

      • high frequency vibrations → travelling waves that maximally displace areas of the membrane closer to the oval window (high-pitch = base of cochlea)

      • low-frequency vibrations —> maximally displace areas of membrane closer to far tip of cochlea. (low-pitch = wide end of cochlea)

  • explains high frequency but not low-frequency

    • high-frequency stimulates a precise area on the basilar membrane

    • low-frequency causes large part of basilar membrane to be displaced, so it’s hard to identify an exact location.

• Frequency theory

  • the perception of a sound’s frequency depends on how often the auditory nerve fires

  • so higher-frequency = more auditory nerve fires

  • limitation: a single neuron has a max firing rate of 1000 times per second.

    • theory doesnt apply to tones with frequencies that require a neuron to fire more rapidly

• Volley principle

  • made to deal with frequency theory’s limitation

  • a cluster of nerve cells can fire neural impulses in rapid succession, producing a volley of impulses

    • more neurons alternate neural firing to attain a combined frequency above the 1000 times/second rate.

how does the brain process auditory information?

• information moves from hair cells in inner ear to auditory nerves, carrying neural impulses to the brain’s auditory areas

• most auditory information from left ear goes to right side of brain, but some also go to the left side of the brain.

• many synapses in ascending auditory pathway

  • most fibres cross over the midline between hemispheres of cerebral cortex.

  • some proceed to hemisphere on the same side as the ear of reception

• auditory nerve extends from cochlea to brain stem

  • some fibres cross over the midline

  • cortical destination of fibres is the temporal lobes

how do cochlear implants work?

transmits external sounds directly to auditory nerve via electrical pulses.

how can we tell where a sound comes from?

• having two ears helps localize a sound

• timing

  • which ear hears the sound first?

• intensity

  • which sound is more intense?

  • which ear is in the sound shadow?

    • Sound shadow: barrier that reduces the sound’s intensity

but what if the sound reaches both ur ears simultaneously?

• pinna has an asymmetrical shape

• sounds behind are distorted differently by pinna than sounds above or in front.

• cells in the brain are keenly tuned to detect these differences so that we can tell where a sound is located

what are the other senses?

what are the skin senses?

skin has receptors for touch, temperature and pain which form the cutaneous senses

how do we feel touch?

• we detect mechanical energy/change in pressure

• energy captured by touch receptors

  • produce action potentials

  • sent information thru spinal cord

  • spinal cord to brain stem

  • information crosses to other side of brain

  • info moves to thalamus (relay station)

  • thalamus projects a map of the body’s surface onto somatosensory areas of the parietal lobes in the cerebral cortex

mirror-touch synaesthesia: sense of touch to the extreme (can feel other ppl’s senses)

how do we feel temperature?

• thermoreceptors respond to changes in temperature

• try to keep body temperature at 37 degrees celsius

• types of thermoreceptors: warm and cold

how and why do we feel pain?

• intense stimulation of any one of the senses can cause pain

• perceiving pain motivates us to stop something that is harmful/inform us that an injury needs our attention

• pain receptors are anatomically similar but differ in the type of stimuli they’re ready to react to

  • mechanical pain receptors: respond to pressure

  • heat pain receptors: temperature

  • other pain receptors: mixed function, responding to both

  • many receptors are chemically sensitive and respond to a range of pain-producing substances

more on pain receptors

• have a much higher threshold fo rfiring than receptors for temperature and touch

• pain receptors react mainly to physical stimuli that distort or chemical stimuli that irritate

  • inflamed joins —> prostaglandins → stimulate receptors causing feeling of pain (Aspirin might help decrease pain)

• Neural pathways that transmit pain messages to brain:

  • Fast: myelinated A-delta fibres connect directly with the thalamus and the motor and sensory areas of cerebral cortex

    • provides immediate info abt an injury, takes less than a second for info to reach cerebral cortex

    • for sharp, localized pain

  • Slow: unmyelinated C fibres transmit pain through limbic system

    • delays arrival of information by seconds

    • unpleasant nagging pain reminds brain that an injury has occurred and need to restrict normal activity and monitor the pain

    • endorphins believed to be released in synapses of slow pathway

what are the chemical senses?

smell and taste

• smell = detect airborne chemicals dissolved in our saliva

how do we taste?

• papillae contain taste buds which are receptors for taste.

• tastes: sweet, sour, bitter, salty, umami (flavour of L-glutamate)

how do we smell?

• olfactory epithelium: lines roof of nasal cavity

  • sheet of receptor cells for smell

• sniffing maximises chances of detecting an odour

• receptor cells covered with millions of minute (antenna that project through the mucus in the top of the nasal cavity and make contact with air on its way to the throat and lungs)

• olfactory nerve carries information about the odour to the brain for further processing

• neural pathway:

  • goes to olfactory areas in the temporal lobes

  • projects to various brain regions esp the limbic system, involved in emotion and memory.

    • smells take a superhighway to emotion and memory

smells might play a role in interpersonal attraction

what are kinesthetic and vestibular senses?

• kinesthetic: provide information about movement, posture and orientation

• vestibular: information about balance and movement

receptors for kinesthetic and vestibular senses are embedded in muscle fibres and joints. as we move, the receptors signal the state of the muscle.

vestibular sense:

• tells us whether our head is tilted, moving, slowing down or speeding up

  • works along with the kinesthetic senses to coordinate proprioceptive feedback (info about the position of our limbs and body parts in relation to other body parts)

  • semicircular canals of the inner ear contain sensory receptors that detect head motion

    • consists of three fluid-filled circular tubes that lie in the three planes of the body (right-left, front-back, up-down)

    • perception of changes in head motion determined by movement of fluid over hair cells in the semicircular canal.

  • vestibular sacs: at the base of semicircular canals

    • utricle and saccule detect sustained changes in head position

    • hair cells in the semicircular canals and vestibular sacs transmit information about movement and head position

pathways:

• starts at auditory nerve, contains both cochlear nerve and vestibular nerve

• axons of vestibular nerve connect with medulla, but some go directly to the cerebellum

• information from sense of vision supplements the combination of kinesthetic and vestibular senses