PSYC102: Topic 4 - Sensation & Perception

Sensation

The reception of stimulation from the environment.

• The detection of physical energy by our sense organs which then relay info to the brain

Perception

Interpretation of the raw sensory information; often an automatic process

• Pattern Recognition and Categorization

• Link sensory info to existing knowledge

Sensation & Perception work through

• Raw Data

• Attention

• Expectations & Previous Knowledge

Transduction

The process of converting an external stimulus into electrical activity within neurons

Sense Receptors

Special cells for converting external stimuli into neural activity

Sensory Adaptation

Activation is greatest when a stimulus is first detected, adapt after some time

Psychophysics

The study of how we perceive sensory stimuli based on their physical characteristics

Absolute threshold

The lowest level of a stimulus needed to be detected by the nervous system 50% of the time

• Biological functions are not consistent from one time to the next

• E.g., faint tone of the same intensity → only heard some of the time

Just Noticeable Difference (JND)

The smallest change in the intensity of a stimulus that we can detect

Weber’s Law

There is a constant proportional relationship between the JND and the original stimulus intensity

Light

Electromagnetic radiation

Wavelengths

We only perceive a narrow range of them,

• different _____ = different colors

• Peak to peak

Sclera

White of the eye

Iris

Coloured part of the eye that contains muscles that control the pupil, controlling how much light enters our eyes

Pupil

Circular hole through which light enters the eye

• Pupillary Reflex: Closing as a reflex response to light or objects

Cornea

Curved, transparent layer covering the iris and pupil. Its shape bends light to focus the incoming visual image at the back of the eye.

Lens

Part of the eye that changes curvature to keep images in focus

• Accommodation: changing shape of the ___ to focus on objects near or far

  • Flat=Distant

  • Fat=Near

Retina

Membrane at the back of the eye responsible for converting light into neural activity

• Fovea: Central portion of the ____, responsible for sharpness of vision

• Like a movie screen onto which light from the world is projected

• Contains 2 types of receptor cells; rods and cones

Rods

Vision at low levels of light, very sensitive

• Long, narrow, enable us to see basic shapes and forms

• Dark adaptation: Time in dark before ____ regain maximum light sensitivity

• 110 million in each of your eyes

Cones

Vision at higher levels of light, sensitive to light and fine detail

• Reading

• Give us our colour vision

• 4.5-7 million in each eye

Photopigments

Chemicals that change following exposure to light.

• Different types of receptor cells contain ____________

Optic nerve

Transmits visual information from the retina to the brain

• The place where it connects to the retina is a blind spot

Ganglion cells

Cells in the retinal circuit that receive neural impulses and transmit information out of the eye

• Axons from optic nerve

Photoreceptors

Different ones have different wavelengths, they have pigments that are sensitive to receiving the light energy

Left Visual Field

• Hits the right half of each eye

Right Visual Field

• Hits the left half of each eye

Trichromatic Theory

Colour vision on 3 primary colours, 3 types of cones with differing photosensitivity

• Colourblindness: Inability to see some of all of the colours

Opponent Process Theory

We perceive colour using opposite cells

• Photoreceptors are linked together in pairs of opposite colours, activation of one prohibits perception of the other

Center-surround cells

Fires when light is presented to a small circular area in a specific location of the retina

Feature Detection Cells

Detect lines and edges

• Simple Cells: Detect lines and edges in very specific locations and orientations

• Complex Cells: Detect lines and edges in less restricted locations (broader)

Bottom-up/Data-Driven Processing

Analysis and integration of basic features into a perceptual unit.

• Hierarchical Organization

  • Form perceptual units through a process of increasingly complex connections between simple units

Parallel Processing

The ability to attend to many sense modalities simultaneously

• E.g., perception of many different features of a lion (e.g., shape, orientation, colour)

• Advantages:

  • Fast processing

  • Allows for top-down processing

    • Each type of processing can be influenced by the others

Top-Down Processing

• When context and higher-level knowledge influence lower level processes

• Use existing knowledge to allow us to understand the world more readily

Gestalt Principles

Give us insight into the ways we perceive form. -

• Focused on the whole rather than the individual parts

• Pattern and object recognition is a problem-solving process

Gestalt; Principle of Simplicity

When we have sensory input our perceptual system usually tries to create a percept that is: simple, orderly, and as stable as possible

Gestalt; Law of Proximity

Objects that are physically close to each other tend to be perceived as unified wholes or groups

Gestalt; Law of Similarity

Similar visual elements form a whole

• Shape, colour, etc.

Gestalt; The Law of Closure

Objects are perceived as whole, even if they are not complete

Gestalt; Law of Good Continuation/Continuity

We tend to perceive objects as forming smooth continuous patterns

Gestalt; Law of Symmetry

Object that are formed around a center point form a group or whole

Gestalt; Law of Figure-Ground Segregation

Tendency to structure the visual field into two parts: a figure and a background

• Bistable percepts: stimuli can be perceived in one of two different ways (but not at the same time)

Motion

• Brain judges it by rapidly comparing visual frames,

• Visual info from one frame is compared to what is processed next

Phi Phenomenon

Perception of motion when stationary objects are flashed in quick succession

Depth Perception

Ability to see spatial relations in three-dimentsions and judge distance

Monocular Depth Cues (one eye)

• Pictorial Cues

  • Relative size, texture, interposition, height, light, linear perspective

• Depth Through Motion: Motion Parallax: Nearby objects will tend to move faster than objects in the distance

Binocular Depth Cues (both eyes)

Brain makes comparisons between eyes

• Binocular disparity: each eye transmits slightly different information to the brain

• Binocular convergence: eyes turn inward to differing degrees when we focus on near objects

Perceptual Constancy

We perceive the properties of objects to be constant even through the stimuli around us change when the viewing circumstances change

• Applies to size, shape, colour

Unconscious Inference

We combine information from the stimulus with other cues from the environment to derive perception

Size Constancy

Our ability to perceive objects as the same size no matter how far away they are from us

Shape Constancy

Our ability to perceive shapes as constant even as objects move or we move in relation to them

• Give us a sense of coherence in the world

Colour Constancy

We perceive colours as (relatively) constant across lighting conditions, even though the actual image differs

• Use cues based on context/background

Agnosia

A failure or deficit in recognizing objects

Prosopagnosia

Deficit in recognizing faces

• “The Man who Mistook His Wife for a Hat”

Apperceptive Agnosia

Deficit in recognizing patterns

• Cant synthesize the parts of a stimulus into a whole

Associative Agnosia

Deficit in associating meaning and a pattern

Sound

Mechanical energy in the form of vibrations traveling through a medium (gas, liquid, solid) transmitted in waves

Frequency

The number of cycles a wave complete in a given time (corresponds to pitch)

• Hz

• Pitch Range: 20-20,000 Hz

  • Higher the cycles/second higher the frequency of the sound

Amplitude

Height of the sound wave

• dB

• Loudness range: 0-160 dB

Outer ear; Pinna

Channels sound

Outer ear; Auditory Canal

Channels sound to eardrum

Outer ear; Eardrum

Thin membrane that vibrates according to the frequency of the sound

Middle Ear

• Hammer, anvil, and stirrup: Vibrate at frequency of the sound; transfer the vibrations to the inner ear

• Contains ossicle bones; transmit vibrations and magnify them

Inner ear; Oval Window

Receives amplified sound from ossicles, which cause vibrations in the fluid of the cochlea

Inner ear; Cochlea

Fluid filled inner cavity receives vibrations

Cochlea; Basilar Membrane

Reacts to the vibrations in the fluid

• Not a uniform structure, narrow and stiff near the base

Cochlea; Organ of Corti

Contains hair cells that are stimulated by different vibrations and perform the process of transduction

Place Theory/Coding

Different frequencies stimulate different locations on Basilar Membrane

• Narrow at base, wide at apex

• Waves selectively vibrate the membrane

• Higher pitch sounds do not travel as far as lower pitch sounds

• 5000-20000 Hz

Frequency Theory/Principle

Tones with different frequencies cause neurons to fire at different rates

• Explains low frequency range for pitch perceptions

  • Can only fire so many times per second

  • Like individual archers

• 100-500 Hz

• Rates of neurons firing

Volley Theory

Sets of neurons fire just out of sync with each other to code for frequency above the rate at which neurons can fire

• Groups of archers

• 500-5000 Hz

• Both frequency and place

Interaural level (intensity) difference

Difference in sound intensity arriving at each ear

• Acoustic shadow: reduction in sound for the far ear

• Best for high freq. sounds

Interaural time difference

Sounds arrive at each ear at different times due to different spatial locations

• More effective for low frequencies

Olfaction

Our sense of smell

Gustation

Our smell of taste

Odors

Airborne chemicals that interact with receptors in the lining of our nasal passages

• Our nose detects between 2,000 and 4,000

Taste bud

Sense receptor in the tongue that responds to:

• Sweet, Salty, Sour, Bitter, Umami

In bumps on the tongue called papillae

Olfactory Neurons

Contain a single type of olfactory receptor, which recognizes an odorant on the basis of its shape

Pheromones

Odorless chemical that serves as aa social signal to members of one’s species

Somatosensory

Sensory of touch, pressure, temperature, and injury

How we sense somatosensory stimuli

• Free Nerve Endings

  • Can be polymodal

  • Are often nociceptors

• Other specialized nerve endings

  • Slow and fast-adapting

  • Many types: can be very specialized

Withdrawal Reflex

Pull away prior to conscious decision

Proprioception

Our sense of body position

• Proprioceptors sense muscle stretch and force

Vestibular sense

Our sense of equilibrium or balance

• Semicircular canals in the inner ear are filled with fluid

• Information is sent to parts of the brainstem that control eye muscles