PSYCH MIDTERM 2

Sensation

the detection of external stimuli and the transmission of this information to the brain

Perception

the processing, organization, and interpretation of sensory signals

The Perceptual Cycle

-Transduction

•Neural processing

•Perception

•Recognition

•Action

•Knowledge

Transduction

turning physical stimuli from the world into neural signals in the brain (action potentials)

Neural processing

original neural signals bound/integrated with others, sent to “higher” areas to be processed further

Perception

an awareness of the experience

Recognition

match current perception with memories

Action

leading you to perhaps do something, which may change future perceptions

Knowledge

previous experiences color current perceptions

Vision

Light waves

Light-sensitive rods and cones in the retina of eye

Optic Nerve

Hearing

Sound Wave

Pressure-sensitive hair cells in cochlea of inner ear

Auditory Nerve

Taste

Molecules dissolved in fluid on the tongue

Cells in taste buds on the tongue

Portions of facial, glosspharyngeal, and vagus nerves

Smell

Molecules dissolved in fluid on membranes in the nose

Sensitive ends of olfactory mucous neurons in the mucous membranes

Olfactory Nerve

Touch

Pressure on the skin

Sensitive ends of ouch neurons in skin

Cranial nerves for touch above the neck, spinal nerves for touch elsewhere

Photoreceptor

Respond to variations in light

Chemoreceptors

responds to chemical

Thermoreceptors

respond to changes in temperature

Nociceptors

Respond to tissue damage- PAIN

Mechanoreceptors

Respond to movement, pressure, tension

Filters

shape perception

Transducers

Stimulus-induced alterations in membrane potentials

Receptor potentials that lead to firing of action potentials in the neural circuit

Taste Buds Detect Chemicals

Gustatory sense

• Uses taste buds to respond to the chemical substances that produce at least five basic sensations: sweet, sour, salty, bitter, and umami (savory, or ‘yummy’)

The number and distribution of taste buds vary among individuals

• Underlying genetics, rather than the number of taste buds, is the major determinant of whether a person is a supertaster. Women, more than men!

Receptors in the Nasal Cavity Gathers Odorants

Olfactory epithelium

Olfactory bulb

Olfactory epithelium

Receptors respond to chemicals and send signals to the olfactory bulb, in the brain

Olfactory Bulb

the brain center for smell, located below the frontal lobes

• Information about whether a smell is pleasant or unpleasant is processed in the brain’s prefrontal cortex.

• The intensity of a smell is processed in brain areas that are also involved in emotion and memory

Receptors in the Skin Detect Pressure, Temperature, and Pain

Haptic sense

Kinesthetic sense

Haptic Sense

– Relies on tactile stimulation to activate receptors for temperature, for sharp and dull pain, and for other sensations

Kinesthetic Sense

-perception of the positions in space and movements of our bodies and our limbs

Pain perception

• Free nerve endings: receptors for pain reside in skin as well as in internal tissues.

• Fast fibers for sharp pain

• Slow fibers register dull, diffuse pain

• Different types of pain results from stimulation of these receptors in different ways.

• Gate control theory: Complex regulation of pain

Ear Detects Sound Waves

• The size and shape of sound waves activate different hair cells in the inner ear

• The receptors’ responses depend on the sound waves’ frequency and timing and on the activated receptors’ location along the basilar membrane

• Vestibular sense: perception of balance determined by receptors in the semi-circular canals of the inner ear.

Visual receptors: Photoreceptors

• Rods and cones

– Receptors in the retina detect different wavelengths of light, sensitive to light

– The lens helps the eye focus the stimulation on the retina for near versus far objects

carry out photo-transduction

Properties of Receptors

Specificity

Sensory adaptation

receptive fields

Specificity

receptors are specific to a modality as well as within a modality

• Specific to one modality: visual or auditory

• Specificity within a modality: wavelengths of lights or frequency of sound

Sensory Adaptation

Sensitivity to signal decreases over time if same stimulus persists.

•Helps detect new stimuli, focus on changes in the environment

Receptive Fields

Receptors have responses based on the spatial localization of the stimulus in the environment

•This results in discrimination between stimuli

Coding

RECEPTORS code Sensory information:

• Sensations are transduced messages carried by nerve impulses to the brain

• Can be quantitative or qualitative

– Firing rate & number of receptors vs. which receptors

• Most qualitative sensory coding involves “coarse coding”

– few receptors responding to range of stimuli

– Brain computes perception by integrating activity across the whole range of receptors

Topographic Organization

Representations in sensory systems are organized based on receptive fields

• Neighboring areas of the body/environment are represented by neighboring sets of neurons

Cortical Magnification

Higher the sensitivity larger the number of neurons (with less overlap in receptive fields!)

-Representation is proportional to sensitivity (or fine control for motor areas)

Signal Detection Theory

a theory of perception based on the idea that the detection of a stimulus requires a judgment—it is not an all-or-nothing process

• research involves a series of trials in which a stimulus is presented in only some trials. In each trial, the participant must state whether he or she sensed the stimulus

• can measure discrimination independent of response bias

Response Bias

a participant’s tendency to report or not report detecting the signal in an ambiguous trial

Discriminability

a measure of how well someone can detect signal from noise

Bottom-up processing

perception based on the physical features of the stimulus

Perceptual processing that relies only on information available in the sensory input

Top-down processing

how knowledge, expectations, or past experiences shape the interpretation of sensory information

Perceptual processing that relies on prior knowledge of the properties of the objects or events to be detected

Qualitative vs. Quantitative Sensory Information

firing different combinations vs firing at different rates

Approaches to the Study of Perception

Behavioral approach

Psychophysical approach

Physiological approach

Behavioral Approach

stimulus ----> perception

• Phenomenological methods (qualitative)

• exclusively used from 300 BC to 1800’s

• Psychophysical methods (quantitative)

• field of science that quantifies the relationship between a stimulus and its perception

• Gustav Fechner, 1800's

• Detection, Discrimination, Scaling

• Physiological approach:

stimulus ----> physiology ----> perception

Psychophysical approach (Psychophysics)

the stimulus-perception relationship

Physiological approach (1)

the stimulus-physiology relationship

Physiological approach (2)

the physiology and perception relationship

Measuring Performance

Sensitivity

Absolute Threshhold

Sensitivity

All sensory systems have a Threshold for responding to stimuli

Absolute threshold

Smallest amount of stimulus energy that can be detected

(Response threshold/ Behavioral threshold/ Detection threshold)

Low threshold = High sensitivity!

Discrimination/Difference threshold

smallest difference in stimulus energy that can be discriminated between two stimuli

Weber’s Law

jnd/S = k

JND is based on relative proportions of stimuli

Stimulus discrimination

• Just noticeable difference: different for different comparison stimuli

• Signal detection theory: can measure discrimination independent of bias!

Magnitude estimation

Determines the relationship between the actual and the perceived intensities for supra-threshold stimuli

Observer compares the standard stimulus to test stimuli by assigning numbers relative to the standard

Stevens’ Law

P = k S^n

Relationship between intensity and perceived magnitude is a power function

Searching for stimuli

• Visual search

• Reaction time

• Response time

Visual Search

observers look for one stimulus in a set of many stimuli

Reaction Time

time from presentation of stimulus to observer’s response is measured

Response Time

gives an estimate of processing time

Feature Search

When searching for a target among distractors… if target differs in only a single feature the target may “pop out”

Conjunction/Conjunctive search

Distractors share more than one feature with the target (but one-at-a-time!)

Each distractor differs along one feature, but the scene has multiple feature distractors

Response Performance Method

Reaction time, response accuracy, stimulus judgments

Physiological Method

Measuring brain activity- Neural recordings, EEG, PET, fMRI, TMS

The Visual System

The structure of the eye is designed to project a sharp image onto the retina, the light-sensitive tissue that lines the back of the eye

Rods

- Outside of the fovea.

– More sensitive to light; operate at night.

– more visual pigment

– more efficient chemical cascade

– saturate in daylight

– Scotopsin more sensitive to lower wavelengths

Cones

- Concentrated in the fovea.

– Less sensitive to light; operate during day

– less visual pigment

– less efficient chemical cascade

– saturate only in intense light

– Photopsin more sensitive to higher wavelengths

– Responsible for color vision: 3 kinds, each sensitive to different wavelengths (color) of light

Processing in the retina

receptor cells, bipolar cells, horizontal cells, ganglion cells, are wired together to detect light edges

Lateral inhibition

Neighboring cells inhibit each other in neural circuits, that results in contrast enhancement at the edges

– Visual systems are sensitive to edges

– If a rod or cone is stimulated, it sends information to its neighboring receptors, inhibiting their activity

Perceiving Objects : Feature Integration Theory

Preattentive stage

Focused attention stage

Preattentive stage

features of objects are separated

Focused attention stage

features are bound into a coherent perception

FFA (fusiform face area) activtity

can predict awareness of face stimuli

PPA (parahippocampal place area) activity

can predict awareness of place/house stimuli

Motion Perception Has Internal and External Cues

• Motion detectors in the cortex respond to stimulation

• The perceptual system establishes a stable frame of reference and relates object movement to it

Stroboscopic movement

– When two or more slightly different images are presented in rapid succession, the illusion of movement occurs

• Moving pictures

Exceptions to the general rule that an image moving on the retina will cause the perception of motion (cont.):

• Brain takes into account movement of the eyes when interpreting movements of the retinal image.

If the retinal image is stationary during a movement of the eyes, the brain will perceive a moving object.

Motion perception: Biological Motion

Coherent motion activated a region matching previous reports of human MT/MST complex located on the temporo-parieto-occipital junction.

Motion Processing Areas of the cortex:

MT,MST,STS Dorsal stream

Consciousness

is each person’s unified and coherent experience of the world around him/her

is a state of awareness of sensations or ideas, such that we can:

– Know what it “feels like” to experience them and reflect on them.

– Report to others that we are aware of these sensations and ideas.

neural correlate

is a change in the nervous system that occurs at the same time as, and may be the biological basis of, a specific mental event or state

levels of conciousness

- Higher-level

- Lower-level

- Altered states of consciousness

- Sub-conscious

- No awareness

A Unitary Experience

Consciousness brings together the fruits of our sensory systems into a unified phenomenological experience that remains continuous over time.

Our awareness of the world is based on a melding of these sensations into a single, multimedia event.

Fundamentals of Cognitive Neuroscience

The central property of consciousness is that we are aware of some mental processes and not aware of others

Includes aspects of being awake and aware

Consciousness has limits

• Access to Information

– Information processing in the brain can be divided into two classes: processes that are accessible to consciousness and processes that are not.

• Consciousness has limits:

– Number of things that can be attended at once is limited

Attention

the process of enhancing our awareness of stimuli that are of interest, while decreasing our awareness of other stimuli (distractors)

Visual attention operates through both automatic and effortful processes

Selective Attention

refers to processes through which we focus on one input or one task while ignoring other stimuli

Some have ADD/ADHD

“Scanning a scene”

Fixations

pauses in eye movements that indicate where a person is looking, focusing/attending • Approximately 3 fixations per second

Characteristics of the scene: Stimulus salience

areas of stimuli that attract attention due to their properties

• Color, contrast, and orientation are relevant properties

• Bottom-up process that is unrelated to meaning

Picture meaning and observer knowledge: Scene schema

prior knowledge about what is found in typical scenes

• Fixations are influenced by this knowledge

Influence of the observer’s task

• Task demands override stimulus saliency

• Eye movements usually precede motor movements by fraction of a second

shadowing

Using headphones, different information is presented to each ear. This is known as dichotic or selective listening

cocktail party effect/popout

The participants own name, or any words of high personal significance, will be noticed even in the unattended channel

Inattentional blindness

When you don’t attend to the specific type of stimulus, you miss large stimuli in the scene

gorilla

Change blindness

When processing is interrupted, you miss large changes in the scene

– color changing cards

Attentional blink

When you are processing something, other stimuli that happen at the same time or closely thereafter may be missed altogether! – gating of information

Divided attention

refers to the skill of performing multiple taskssimultaneously.

• This is only possible when the sum of the tasks’ demands is within the “cognitive budget.”

The Stroop Effect

A classic interactive demonstration of what happens when automatic processes (reading) interfere with controlled tasks (naming colors).

Real-World Failure Points

The Multitasking Myth

Automaticity Interference

Missing the Gist