PSYC 100

Colour constancy

Under changing light conditions, the brain adjusts its perception of colour to remain constant (Ex: white shirt remains white in our brains even under harsh red lighting that actually makes it a different color)

Sensation

Stimulus energies received from the environment and converted into action potentials that can be perceived by the nervous system

Transduction

• The conversion of stimuli into electrical energy (action potential)

  •  the action potential is then sent to the brain via sensory nerves.

  • Different process for each sensory organ

    • but sends the same kind of electrical energy (action potential

Perception

• The processing of sensations, organizing, constructing, and interpreting them to form a representation 

• This representation is formed by the brain to serve as a model of what is outside

  • based on prior experiences and present sensory evidence

  • cannot be trusted as a direct copy or true “reality”

What does top down processing use when processing sensory information from the bottom top perception? 

Prior experience, knowledge, expectations

Psychophysics

• A field that focuses on the relationship between physical characteristics of environmental stimuli (magnitude) and our mental experience of them (perceived intensity)

  • study of physical vs mental experience

Absolute threshold of awareness

• The minimum amount of stimulation needed for a person to detect a particular stimulus half of the time

• Opposite of sensitivity

What is the relationship between absolute awareness threshold and sensitivity?

• Lower threshold = higher sensitivity

• Lower sensitivity = higher threshold

Signal detection theory

An approach in measuring thresholds that takes into account both the intensity of the stimulus and psychological biases for a more accurate assessment

Conservative bias

I hear nothing

Hits

Responding yes when a stimulus is present

Misses

Responding no when a stimulus is present

False alarm

Responding yes when there is no stimulus present

Correct rejection

Saying no when no stimulus is present

Just-noticeable difference

The minimum change in a stimulus for an observer to detect a difference half the time

Weber’s law

The perception of a stimulus change is proportional to the magnitude of the stimuli

While you are on vacation with your brother, he tells you about a psychological study he recently participated in. When he was holding a 50-gram weight, he couldn’t tell that extra weight had been added until the added weight was more than 5 grams. According to Weber’s Law, how much of your stuff can you add to his 25-kilogram suitcase without his noticing?

The ratio of 5 g to 50 g (in the study) is the same as 2.5 kg to 25 kg.

Adaptation

A stimulus remains constant over times and eventually seems to disappear

Benefits of sensory adaptation (level of sensory receptors) and perceptual adaptation (higher up in the brain)

Frees us to focus on changes in our environment rather than unchanging stimuli

Properties of light

Wavelength, frequency, amplitude, co

Photoreceptor

Cells called rods and cones. When light energy hits them, it causes chemical changes in photopigments and changes their shape

Cones

• High-resolution colour vision

• densely clustered in a small central pit in back of the retina – fovea (small pit in the centre of retina packed with cones)

• Acuity, sharpness or specificity of perception, supporting the discrimination of stimuli. contain ⅓ varieties of photopigment, colour vision only occurs here

• Less than rod cells.

• demonstrates less convergence than rods because they have a 1-1 ratio of cones per ganglion cells

Rods

• photoreceptor cells that primarily

  support nighttime vision

• Sensitivity, ability to detect a stimulus is present

• Can offer more sensitivity in low light because there are more of them.

• Contain rhodopsin.

• All have the same type of photopigment.

• Demonstrate a much greater degree of convergence, connecting many individual signals to one ganglion cell

Visual transduction

Rods and cones converting light into electrical energy.

When light energy hits rods and cones, it causes chemical changes in photopigments and changes their shape. This then alters flow of ions. This change in ionic concentration generates electricity, which is passed on to layers deeper in the retina—the bipolar cells and then the ganglion cells, which fire action potentials when stimulated sufficiently.

Rhodopsin

An extremely light-sensitive pigment that allows us to see in the dark. Rod photochemical: Breaks down and becomes inactive when exposed to bright light. Regenerates in the dark

What property of cones allow colour vision

Photopigment

Trichromatic theory of colour vision

Cones provide the information to give us colour vision by 3 types of receptors working together to produce perception of multicoloured world

Each type of cone photopigment is most sensitive to ⅓ wavelengths

Long wavelengths (L) = red

Short (S) = blue

Medium (M) = green

A single cone type cannot distinguish precise wavelength & amplitude of light– joint effort, needs 2, and then more information to decipher signals coming from 2 cones

Opponent process theory

• A theory of colour perception that states:

  • information from the cones is separated into three sets of opponent channels in the ganglion cell layer

    • red & green

    • blue & yellow

  • Responses of the cones are combined in the bipolar and ganglion cell layers

  • Colour opponency is due to how bipolar cells combine inputs from different cone types.

Feature detectors

Specialized cells in the visual cortex that respond to basic features such as lines, edges, and angles– building blocks of perceptual experience

Visual association cortex

Region of the brain where objects are reconstructed from prior knowledge & information collected by the feature detectors

Visual agnosia

• An impairment that causes prevents a person from recognizing objects in spite of having the ability to see them

• 2 Types:

  • Apprehensive

  • Associative

Prosopagnosia

• a neurological or developmental disorder causing an inability to recognize the identity of faces, despite normal vision and intelligence

Ventral pathway

• Travels along temporal lobe

• addresses “what” questions

• Responsible for recognizing objects and faces

• Damage here leads to visual agnosia, where subject is not able to recognize object

Dorsal pathway

• Flows up to the parietal lobe

• Projects from V1 to the posterior parietal cortex

• answers “where” and “how” questions

• handles:

  • spatial location

  • depth

  • movement

  • visually guided actions  

• Responsible for determining location and the perception of movement

• Damage here may result in seeing movement as series of statistic “snapshots”, not smooth or predictable

Gestalt psychology

• A school of thought

• Gestalt means “form”

• Argues that perception is more than just piecing together building blocks

  •  Ex: Connectedness, closure, continuity, proximity, similarity, synchrony, these are all patterns and experiences we see and feel through our perception that goes beyond our experience of consciousness 

Illusory contours

Boundaries of objects that are not visible, but are implied by the arrangement of line segments and other visual stimuli

Binocular cues

Depth information gathered from the separation between an individual’s two eyes, allowing the brain to receive two perspectives on the same event

Monocular cues

Depth information that can be gathered by only one eye.

Relative size, relative height, interposition, linear perspective, relative motion

Components of the ear

• Pinna

• ear canal

• ossicles

• eardrum

• oval window

• basilar membrane

Pitch

Quality of a sound, highness or lowness

Receptors that give rise to tactile sensations

Epidermis

Where and how are touch sensations recieved throughout the body organized in the brain

Temperature, pressure, vibration, pain

Tactile agnosia

the inability to recognize objects by touch

Brain regions which may be damaged in an individual with tactile agnosia

Parietal lobe

Interoception

Ability to perceive signals originating within the body (breathing, hunger, thirst). Crucial for being able to maintain steady internal state.

Insula

Plays key role in processing these signals, imbues them with emotional & motivational significance. E.g., may interpret signals of sympathetic nervous system activation as anxiety

Proprioception

Sensory system responsible for awareness of body positions (impaired by alcohol). The sense of how each body part is arranged in relation to the rest.

How the vestibular system works

Balance, vestibular fluid

How conflict between vestibular and visual systems can create motion sickness

Vestibulo-ocular reflex(VOR)= reflex that helps stabilize your gaze during head movements. Signal travels from semicircular canals to the brainstem, which then coordinates eye muscles to move eyes in opposite direction of head movement. Mismatch between senses can lead to motion sickness.

Transduction of olfactory stimuli

The epithelium sends signals to the olfactory bulb, and it is here that the first clear structure emerges in olfaction. Signals are sent to glomeruli, spherical clusters of neurons that respond differently to different types of stimulus.

Transduction of gustatory stimuli

3 nerve tracts that connect tongue to brain, after passing through a specialised gustatory region of the thalamus, taste information is directed to the primary gustatory cortex located in insular cortex.

Where taste information is processed in the brain

Primary gustatory cortex / insular cortex

McGurk effect

Lip movements change what we hear

Outer Ear

•  Made up of the pinna

• sound funnel with evolved shape to capture sound waves

Ear canal

• Helps enhance certain sound frequencies and protects eardrum / tympanic membrane (boundary line between outer and middle ear)

Ossicles

• 3 of tiniest bones in the human body

• part of the middle ear

• malleus (hammer), incus (anvil), stapes (stirrup) forming a bridge between eardrum and oval window

  • they act as levers to amplify incoming sound waves

Cochlea

Shell-shaped critical transducer of the ear, turns fluid vibrations into neural energy. Coil is filled with fluid that is moved when ossicles push and pull on the oval window

Basilar membrane

Contains auditory cilia / auditory sensory neurons, movement of cochlea fluid that causes cilia to bend and trigger neural impulses

Auditory nerve

Axons of hair cells from cochlea are bundled together to form this, where action potentials from the hair cells travel through to the brain stem, which transmits the impulses through the auditory nucleus of the thalamus up to the primary auditory cortex in the temporal lobe.

Visual wavelength

What we experience as colour

Frequency

Number of cycles per second of a wave

Visual amplitude

• Height of the crests of a wave

• Maximum height of a light wave,

  • related to experience of intensity and brightness– which in turn distinguish the quality (colour) and quantity (brightness) of light

Colour purity

Related to the number of wavelengths that make up the light. Determines quality of a colour’s saturation. Spectral colours are the most pure and vivid (smallest number of wavelengths) – when mixed together or with white light, results in range of distinguishable colour experiences. The more wavelengths sensed, the less colour you see.

Cornea

• Where light first enters your eye

• a transparent covering at the front of eye

Pupil

Light passes through, a whole in the muscle known as the iris, appears black because most of the light entering the pupil is absorbed  like a black hole by the inner tissues of the eye

Iris

• Part of the eye

• colored muscle surrounding the pupil (has a circle/ring shape)

• controls the amount of light entering the eye

Lens

• Focuses light on retina, bends light and using a process called accommodation:

  • adjustment of the lens’s thickness by specialized muscles in order to change the degree to which it bends light.

• gets less elastic over time and weakened focus via accommodation

Retina

• A surface on the back of the idea that contains photoreceptor cells (cones and rods, sensitive to light)

Accommodation

Adjustments of the lens’s thickness by specialized muscles in order to change the degree to which it bends light. Lens becomes elastic with age

Three types of neurons

Sensory neurons, motor neurons, interneurons

Sensory neurons

Carry messages from the sensory organs to spinal cord and brain

Myelin sheath

Fatty layer that insulates the axons and speeds up the transmission of electrical signals

Glial cells

• Nervous system cells

• Has a variety of functions, ex:

  •  providing structure for neurons

  • providing nutrition for neurons by releasing things they need

How do myelin sheath and glial cells support neuronal functioning

Form tight collections with blood vessels to form blood-brain barrier, nutrient supply, insulation, pruning unneeded connections

Action potential

Neurons “talk” to each other by firing off electrical impulses called action potentials. Action potentials generated at the junction between the axon and cell body. Travel down the length of the axon to its terminal, where they signal release of chemical messages to neighbouring cells

Cell membrane

Thin fatty skin enclosing neuron, separating between intracellular fluid inside neuron and extracellular fluid outside neuron which contain electrically charged particles / ions

Resting potential

Neuron cannot fire action potential in this state, more negatively charged particles inside cell relative to outside— resting potential / electrical charge across the membrane is -70 millivolts.

Depolarization

When neuron sufficiently stimulated by other neurons, opening of ion channels in the cell membrane at end of axon adjacent to soma. Ion channels allow positively charged sodium ions to enter. Electrical charge across membrane begins to reverse

Becomes less negative. If the threshold is reached, voltage-gated sodium channels open. Na⁺ rushes into the cell, causing the membrane potential to rapidly rise, often peaking around +30 mV.

Repolarization

After the peak, sodium channels close, and voltage-gated potassium channels open. K⁺ exits the cell, returning the membrane potential back toward the resting state.

Refractory period

Period of time required for a neuron to return to its resting state before it can fire another action potential

Synaptic cleft / synapse

Gap seperating neurons / spans the axon terminals of the sending neuron with the dendrites or cell body of the receiving neuron. An anatomical impasse, like the edge of a canyon with no bridge for crossing to the other side.

Neurotransmission

Allows the electrical message to bridge the synaptic gap by converting the electrical signal into a chemical one, thus allowing neurons to transmit their signals to one another.

Receptor

Channel in membrane of a neuron that binds neurotransmitters in ”lock-and-key” fashion

Cross-synaptic communication

The process of neurotransmission allows the electrical message to bridge the synaptic gap by converting the electrical signal into a chemical one, thus allowing neurons to transmit their signals to one another.

What are the steps of an action potential forming?

• Starts at resting potential, -70 mV

• stimulus causes a reduction in charge difference inside (-) vs outside (+) called depolarization

• repolarization, the change in charge slowly returns

• hyperpolarization, the cell overshoots and goes beyond -70 mV, increasing the difference in charge across the membrane more than normal

• Neuron returns to resting potential from hyperpolarization

How action potentials are converted from electrical signals into chemical signals

Synapse— junction between two neurons or between a neuron and a target cell.

Presynaptic neuron sends chemical messengers called neurotransmitters

Arrival of the action potential triggers release of neurotransmitters stored in the axon terminal

Neurotransmitters cross gap & bind to receptors on the postsynaptic neuron.

How neurotransmitters get removed from the synaptic cleft

Diffusion=neurotransmitters drift out of synapse

Degradation= neurotransmitters are broken down in the synapse

Reuptake= neurotransmitters are reabsorbed into the presynaptic terminal branches

Excitatory signals

Move the voltage of the neuron closer to its threshold

Inhibitory signals

Move the voltage of the neuron farther to its threshold

GABA

Most common inhibitory neurotransmitter. Downregulation of stress, anxiety, fear. Many sedative drugs act by targeting its receptors. Alcohol also promotes activity at receptors

Acetylcholine

Can trigger both excitatory and inhibitory signals. It's commonly found at the neuromuscular junction, where drugs like curare, used as bioweapons, can interfere. Crucial role in the autonomic nervous system, regulating communication between the brain, glands, and organs, as well as cardiac activity. Learning and memory— low levels associated with dementia / Alzheimers

Norepinephrine

Important for “fight or flight response”. Contributes to arousal & vigilance. In excess, can contribute to high blood pressure, anxiety

Serotonin

Contributes to regulation of sleep, appetite, mood, and aggression. Thought to play in depression, although precise mechanism still debated

Dopamine

Involved in movement, planning, and aspects of reward. Most addictive drugs stimulate increased activity in dopaminergic circuits. Excess levels associated with schizophrenia, low levels with Parkinson’s disease

Endorphins

• “Endogenous morphine”

• Promotes feelings of pleasure 

• Reduces pain

Psychoactive drugs

chemical substances that alter a person’s thoughts, feelings, or behaviors by influencing the activity of neurotransmitters in the nervous system