Sensation and Perception in Psychology (Units 1-4)

Are there really five senses?

No — the idea of five senses (sight, sound, smell, taste, touch) comes from Aristotle. Modern science shows we have more, including balance, pain, temperature, proprioception, and itch.

What is sensation?

Sensation is the process by which sensory organs detect physical energy from the environment and convert it into neural signals sent to the brain.

What is perception?

Perception is how the brain organizes and interprets sensory information to form a meaningful experience.

Neural transduction: receptors, transduction and neural response

Neural transduction is the conversion of a physical stimulus (like light or sound) into a neural signal via specialized receptors, which then send information to the brain.

What is phenomenology?

Phenomenology refers to a person's unique, subjective experience of the world — what it's like to see, hear, or feel something personally.

Aristotle and the five senses

Aristotle identified five senses, but also observed illusions like the motion aftereffect and the Aristotle illusion, showing that perception can be misleading.

Thomas Young: colors are coded by three different kinds of nerve fibers

Thomas Young proposed that color vision is based on three types of receptors, laying the groundwork for the trichromatic theory of color vision.

Johannes Mueller: doctrine of specific nerve energies

Johannes Mueller developed the doctrine of specific nerve energies, which says that different sensory systems respond to different kinds of information, regardless of how they're stimulated.

Von Helmholtz:

Helmholtz believed perception is a combination of sensory input and mental processes, including unconscious inference — our brain fills in gaps automatically based on past experience.

perception is constructed from both senses and cognitive processes

Hering proposed that color is perceived through pairs of opposing colors (red-green and blue-yellow), suggesting there are four primary colors instead of three.

unconscious inference

Weber's Law states that the just-noticeable difference between two stimuli is proportional to the intensity of the original stimulus.

three basic color receptors (like Young)

Fechner is known as the father of psychophysics. He studied how physical stimulus intensity relates to perceived intensity.

Hering: colors are perceived through 2 pairs of opposing colors (four primary colors, not three)

Fechner's Law says that sensation increases logarithmically with physical stimulus intensity — meaning it grows slower as intensity increases.

Weber's Law: the just-noticeable difference between two stimuli is related to the magnitude or strength of the stimuli.

Gestalt psychology emphasizes that we perceive whole patterns or configurations, not just individual sensory inputs.

Fechner: father of psychophysics, the study of the relation between physical stimuli and the perception they elicit.

Law of Proximity: Objects that are close together are perceived as belonging to a group.

Fechner's law: sensation is a logarithmic function of physical intensity

Law of Common Fate: Things moving in the same direction appear to be grouped.

Gestalt psychology: The whole is larger than the sum of its parts

Law of Closure: Our brains fill in missing parts of a figure to see a complete image.

Gestalt laws:

Law of Similarity: Similar items are grouped together in perception.

Law of Proximity

Law of Good Continuation: We perceive smooth, continuous lines rather than disjointed ones.

Law of Common Fate

Gibson's theory of direct perception suggests that all information needed for perception is present in the environment — no need for cognitive processing.

Law of Closure

The Information Processing Approach explains perception as a sequence of steps involving sensory input, processing, and output.

Law of Similarity

The Computational Approach studies the computations the brain performs to turn sensory input into perception.

Law of Good Continuation

Neuroscience in perception focuses on how the brain's structures process sensory signals.

Gibson and Direct Perception

Microelectrodes are tiny wires used to measure electrical activity from neurons.

Information Processing Approach

Neuropsychology studies how brain injuries affect perception and behavior — e.g., agnosia and prosopagnosia.

Computational Approach

EEG measures electrical activity in the brain using electrodes on the scalp.

Neuroscience in Sensation and Perception (brain organization)

fMRI measures brain activity by detecting changes in blood flow.

Methodologies in Neuroscience

A psychophysical scale relates physical stimulus strength to perceived intensity.

Microelectrode

An absolute threshold is the smallest amount of a stimulus needed to detect it 50% of the time.

Neuropsychology: agnosia, prosopagnosia

Method of Limits presents stimuli in increasing or decreasing order to find the threshold.

Electroencephalography (EEG)

Method of Constant Stimuli presents stimuli in random order to find the detection threshold.

Functional MRI (fMRI)

In the Method of Adjustment, the participant changes the stimulus to find when it is just detectable.

What is a Psychophysical Scale

Sensitivity refers to how well someone can detect a stimulus or difference.

Absolute Threshold

Magnitude estimation is when participants assign numerical values to the strength of a stimulus.

Method of Limits (using crossover points)

Stevens' Power Law says the perceived intensity of a stimulus follows a power function of actual intensity.

Method of Constant Stimuli (50% detection)

Catch trials are used to check for false positives by including trials with no stimulus.

Method of Adjustment (observer adjusts)

Signal Detection Theory helps us understand how we detect signals under uncertainty — accounting for both hits and false alarms.

Sensitivity

The criterion is a person's internal decision rule — how much evidence they need to say a stimulus is present.

Magnitude Estimation

d-prime (d′) measures sensitivity — how well someone can distinguish signal from noise.

Steven's Power Law

A hit is when the signal is present and the person says it is.

Catch Trials and Their Use

A miss is when the signal is present but the person fails to detect it.

Signal Detection Theory

A false alarm is when the signal is absent but the person thinks it's there.

Criterion

A correct rejection is when there is no signal and the person correctly says so.

d prime

The Receiver Operating Characteristic (ROC) curve shows how hits and false alarms trade off at different criteria.

Miss

Changes in criterion affect response bias — more liberal or conservative decisions.

False Alarm

Differences in d-prime reflect how easily someone can tell signal from noise — higher d′ means better detection.

Correct Rejection

When no signal is present and the observer correctly reports that no signal was detected.

Receiver Operating Characteristic

A plot that shows the trade-off between hit rate and false alarm rate, used to evaluate the performance of a signal detection system.

Changes in Criterion

Shifting the decision threshold (liberal vs. conservative) can increase hits or reduce false alarms depending on the goal or risk.

Differences in Sensitivity (d prime)

A measure of how well someone can distinguish signal from noise — higher d′ means better discrimination and fewer errors.

The sense of Touch includes a variety of sensations

Touch includes pressure, vibration, temperature, pain, itch, and pleasant touch — all detected by different receptors in the skin.

Touch receptors

These include thermoreceptors, mechanoreceptors, nociceptors, kinesthetic receptors, itch receptors, and gentle touch receptors — each specialized for detecting specific types of sensory input from the skin.

Thermoreceptors

Receptors that detect changes in skin temperature. They help us sense warmth or cold and are essential for thermoregulation.

Mechanoreceptors

Receptors in the skin that respond to pressure, vibration, and texture. There are four main types: SA I, SA II, FA I, and FA II.

Kinesthetic receptors

These receptors are located in muscles, tendons, and joints. They help you sense the position and movement of your limbs — a process called proprioception.

Nociceptors

Specialized sensory receptors that detect tissue damage or potentially harmful stimuli, sending signals that are interpreted as pain.

Itch receptors

These receptors respond specifically to itch-inducing stimuli like histamines. They signal the brain to produce the sensation of itch, distinct from pain or touch.

Pleasant/Gentle touch receptors

These receptors, like C-tactile fibers, respond to slow, light stroking touch and are associated with emotional and social bonding.

The Skin and Its Receptors

The skin contains mechanoreceptors, thermoreceptors, nociceptors, itch receptors, and gentle touch receptors — each responsible for detecting different stimuli.

Understand the 4 types of Mechanoreceptors

SA I (texture, pattern), SA II (skin stretch), FA I (slip, grip control), FA II (vibration, deep pressure).

What is proprioception?

Proprioception is your sense of body position and movement, provided by receptors in muscles, joints, and tendons.

Muscle spindles

Receptors in muscles that detect changes in muscle length and help control movement.

Joint receptors

Receptors located in joints that provide feedback on joint position and movement.

Golgi tendon organs

Receptors that sense changes in muscle tension and protect muscles from excessive force.

alcohol consumption affects proprioception

Alcohol impairs proprioceptive accuracy, leading to poor coordination and balance.

Pinocchio illusion

A perceptual illusion caused by conflicting sensory input about body position — e.g., touching your nose while vibrating the bicep tendon makes your nose feel longer.

Patient: Ian Waterman

Ian lost proprioception due to illness and must visually monitor his movements, showing how critical proprioception is for motor control.

Definition of Pain

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage.

Nociceptive pain

Pain from physical damage or potential harm to body tissues, detected by nociceptors.

Where nociceptors can be found

Found in skin, muscles, joints, and some internal organs.

Other Types of Pain

Includes neuropathic, inflammatory, emotional, and empathy-related pain.

Neuropathic pain

Pain caused by damage to nerves or the nervous system, not from physical injury.

Inflammatory pain

Pain resulting from the body's immune response, involving swelling and inflammation.

Empathy pain

Feeling distress when observing another in pain — activates some of the same brain areas involved in personal pain.

Emotional pain

A form of psychological pain (e.g., grief or heartbreak) that activates similar brain networks to physical pain.

Difference between A-delta fibers and C-fibers

A-delta fibers transmit sharp, quick pain; C-fibers transmit dull, aching pain more slowly.

No Pain Sensation? Melzack and Wall (1988)'s study

Their research showed that pain can be inhibited by descending signals from the brain, forming the basis of the Gate Control Theory.

What are the Two Pain Pathways to the Brain

The spinothalamic pathway (sensory/discriminative) and spinoreticular pathway (emotional/motivational).

Somatosensory Cortex

Processes the location and intensity of touch and pain; it's somatotopically organized.

Somatotopic map

A brain map where each body part is represented in proportion to sensory input, shown in the sensory homunculus.

The Homunculus

A visual representation of the body based on the sensory cortex — larger body parts mean more sensory neurons.

Phantom limb syndrome

The sensation that an amputated limb is still present; often includes pain or tingling.

Suborganization of the Somatosensory Cortex

Includes regions for identifying the nature of touch (the 'what') and spatial location (the 'where').

The "What" Channel

Pathway in the somatosensory cortex that helps identify what is being touched.

The "Where" Channel: Correcting Grip

This pathway helps locate where touch occurs and adjusts motor output accordingly.

Pathways of pain

Pain signals travel via the spinal cord to the brain through ascending tracts, primarily the spinothalamic and spinoreticular tracts.

Gate Control Theory

The theory that non-painful input closes the nerve 'gates' to painful input, reducing pain perception.

Implications of Gate Control Theory

Explains why rubbing a wound or applying pressure can reduce pain — these actions 'close the gate'.

Over-sensitization vs. desensitization

Over-sensitization increases pain response, while desensitization decreases it, often due to repeated exposure or neural adaptation.

Role of Anterior cingulate cortex (ACC) in pain perception

The ACC processes the emotional and cognitive aspects of pain, including suffering and unpleasantness.

Role of Prefrontal cortex in pain perception

Involved in evaluating and anticipating pain, particularly with chronic or long-term pain experiences.

The Neurochemistry of Pain: Endogenous Opioids

The body's natural painkillers, including endorphins, which block pain signals in the nervous system.

Analgesia

The reduction or elimination of pain, often through medication or endogenous opioid release.

Runner's high

A feeling of euphoria and reduced pain perception during intense aerobic exercise, linked to endorphin release.

Other chemicals - Addiction risk

Substances like opioids relieve pain but can lead to tolerance and addiction due to their action on reward pathways.

The Perception of Itch

Itch is a distinct sensory experience, separate from pain, triggered by specific pruriceptors and often associated with immune responses.

Pruriceptors

Specialized receptors that respond to itch-inducing stimuli such as histamine and trigger the sensation of itch.

Gentle Touch

A type of social and emotional touch that feels pleasant, often involving slow stroking detected by C-tactile fibers.

Mechanisms of pleasant touch

Pleasant touch is processed by C-tactile afferents, which project to areas of the brain related to emotion and social bonding.

brain regions related to the pleasant touch

Includes the insular cortex, which processes affective and emotional responses to soft touch.