Week 4 & 5: Sensation and Perception

Sensation

The detection of physical energy by the sense organs.

Perception

The organization and interpretation of sensory information by the brain.

Process of receiving sensory information to perception

Stimuli, Sensory receptors, Attention, Interpretation, Response, Perception.

Psychophysics

Examines how physical stimuli affect and interact with mental processes.

Webber

Created psychophysics. The first person to study human response to physical stimulus quantitatively.

Fechner

Created psychophysics. A student of Webber, noticed that different individuals have different sensitivity to stimuli.

Webber’s Law

The Just Noticeable Difference (JND) depends on the percentage change in the stimulus.

Absolute threshold

Difference between not being able to perceive a stimulus and being just barely able to perceive it.

Difference threshold

Measure of smallest change in physical stimulus required to produce a Just Noticeable Difference (JND).

Just Noticeable Difference (JND)

The amount of difference required to recognize two objects are not the same.

Signal detection theory

Recognizes that a stimulus is either present or absent.

Transduction

The external sensory stimulus is converted by a sense receptor into neural activity.

Sensory adaptation

Becoming less sensitive to an unchanging stimulus over time.

Subliminal information processing

The processing of sensory information below conscious awareness. Can create short-term impact on behaviour and attitude but the effect disappears when a person is aware.

Figure -Ground Principle

Visual field perceived in terms of object against background.

Gestalt principles of perceptual organization

Similarity
: Stimuli with similar characteristics are perceived as one.

Proximity
: Objects close together in time or space are perceived as belonging together.

Continuity
: Perceiving objects and belonging together in a continuous pattern.

Closure
: If parts of a figure are missing, it can be perceived as a whole.

Perpetual constancy

We can view people and objects from different angles, distances, and lighting conditions but the object can still be seen as the same size, shape, brightness, and colour.

Bottom-up processing

The whole perceived object is made from parts of stimulus detected from sensory receptors and the brain (What am I seeing?). Ex. patient tries to decipher doctor’s handwriting.

Top-down processing

The whole is modified by experiences, expectations, and goals (Have I seen this before?). Ex. pharmacist can decipher doctor’s handwriting.

Attention - Influence on processing

The process of sorting sensations and selecting some for further processing. Includes inattentional blindness, selective, and divided.

Sclera

White portion of the eye.

Iris

Coloured portion of the eye that controls how much light enters the eye. Muscles dilate and contract pupil through reflex.

Pupil

Hole where light enters the eye.

Cornea

Transparent protective layer that bends light rays inwards into the pupil.

Lens

Contains sensory receptors for vision, responsible for keeping images focused onto the retina. Image projected onto retina is upside down reversed left to right.

Retina

Membrane at the back of the eye.

Fovea

Centre of the eye responsible for acuity (sharpness of vision).

Myopia

Nearsightedness (can see closer objects clearly, distant objects blurry).

Hyperopia

Farsightedness (can see distant objects clearly, closer objects blurry).

Rods

Light sensitive receptors in retina, responds to black and white.

Cons

Receptor cells in retina, help see colour and fine details.

Pathway of sensory information

From eye to occipital lobe, from retinal image to meaningful information, how we make meaning of sensory information.

Frequency

Number of cycles completed by sound wave in one second.

Amplitude

Loudness of sound.

Pitch

High or low of sound, determined by the number of cycles completed per second.

Timbre

Distinct quality of a sound (differs from other similar sounds).

Decibel

A measurement for the loudness of a sound.

Outer ear

Pinna
: Visible curved flap of cartilage and skin.

Auditory Canal
: 2.5 cm long, lined with hairs. Leads to eardrum.

Eardrum
: ~1 cm diameter, thin, and flexible membrane. Moves in response to sound waves.

Middle ear

Ossicles
: Inside chambers of middle ear. 3 smallest bones (hammer, anvil, and stirrup), size of rice grain. Links eardrum to oval window. Amplify sound 22 times.

Cochlea (inner ear)

: Fluid-filled, snail-shaped, bony chamber. Stirrup pushes against oval window, vibrations move cochlear fluid in waves. Produces electrical impulses transmitted to the brain.

Vestibular system

Responsible for sense of balance and awareness of space. Connected to the amygdala, brainstem, and insula. Consists of the vestibular sacs (detects head’s position) and fluid filled semicircular canals (senses rotation of head).

Somatosensory system

Responds to stimuli applied to skin, temperature, and injury. Involves specialized nerve endings (mechanoreceptors) and free nerve endings.

Sense of touch

Nerve endings in skin sends message through nerve connections to spinal cord. Message goes up the spinal cord through the brainstem and midbrain to the somatosensory cortex.

Pain sensation

Nerve endings on the surface of skin that are very sensitive to stimuli. The Gate Control Model argues that neural mechanisms in the spinal cord regulate conscious awareness of pain.

Acute pain

Has an identifiable source and is time-limited.

Chronic pain

Longly unrelieved pain that is a disease itself.

Role of the brain in pain

Gives meaning to pain messages by making it a conscious and emotional experience through the cerebral cortex and limbic system. Can release endorphins (natural pain killers).

The Gustatory System

Sense of taste. Four basic tastes include sweet, sour, savoury, and spicy. Also, umami. There are non-tasters (-), medium tasters (2x), and supertasters (4x).

Papillae

• 4 types, 3 types have taste buds

• Each taste bud has 60-100 receptors

• Lifespan of receptors is 10 days

Olfactory and gustatory perception

Work together to enhance the disliking and liking to certain food. Described as “chemical senses.”

Olfaction

Sense of smell.

Olfactory Epithelium

: Patch of tissue on top of nasal cavity with 10 million smell receptors.

Olfactory Bulbs

: Above nasal cavities, where sensation of smell first registers into the brain.