Sensation and Perception

Psych 1010 - Test 2 Chapter 4 + 5 

Sensation vs. Perception

• Sensation

  • The process of detecting external events with sense organs and turning those stimuli into neural signals.

  • Example: Light waves hitting your eyes; sound waves hitting your eardrums.

• Hearing a voice is air moving against the ear, and seeing someone is light reaching the eyes. The brain then interprets this information where perception happens.

• Perception

  • Involves attending, organizing and interpreting stimuli that we sense. 

  • your brain organizes sounds so you know it’s a person’s voice and combines what your eyes see so you recognize someone walking toward you.

  • Example: Recognizing a friend’s voice or seeing someone walking toward you.

• Transduction: 

  • when specialized receptors transform the physical energy of the outside world into neural impulses. 

• Distinction

  • Sensation and perception can be separate, with examples including illusions and prosopagnosia.

• Process flow: Sensory receptors > thalamus > cortex.

Brain Organization of Sensory Information:

• All senses use the same transmission method: action potentials.
  
  

• Separation of senses: Different sensory signals go to specific brain areas:
  
  

  • Vision → Occipital lobes
    
    

  • Hearing → Temporal lobes
    
    

  • Touch, taste, smell → other specialized areas
    
    

• Key idea: It’s where the brain processes the signal, not just the raw input, that determines perception.
  
  

• Historical concept: Doctrine of specific nerve energies (Johannes Müller, 1826) – each sensory pathway has a specific role in perception.

Perception as a Learned Skill (Development)

1. Infant State: Sensory pathways are not fully clear initially. For example, spoken language (hearing) also activates brain areas related to vision (overlapping sensations).

   • Source: McMaster University research (Maurer & Maurer, 1988).

2. Timeline: This overlap does not disappear until age three.

3. Mechanism: Pathways become clear because less-useful connections are pruned away as the child grows.

   • Conclusion: This shows that perception is a skill that our brains learn through experience, refining the separation of the senses.

Receptor Responsiveness: Sensory receptors are most responsive upon initial exposure to a stimulus.

Cause of Response: Our sensory receptors and brain areas are highly sensitive to change in our environment.

The Response: Changes in the sensory world elicit an orienting response.

Function: The orienting response allows us to quickly shift our attention to new or altered stimuli.

Example: The initial feeling of intense sound from traffic or bright sunlight when you first walk outside. (This sets up the next concept in the full reading: sensory adaptation, which is the opposite reaction to a stimulus that doesn't change).

​​Sensory Adaptation: This is the reduction of activity in sensory receptors with repeated exposure to a stimulus.

• The Process: We allocate progressively less attention to stimuli that remain the same over time. Unchanging stimuli elicit less activity in the nervous system.

• The Effect: The stimulus is perceived as being less intense over time.

• Example: The sound of traffic or bright light seems less intense after a few minutes than it did initially.

Stimulus Thresholds

• Psychophysics

  • The field of study that explores how physical energy such as light and sound and their intensity relate to psychological experience

  • Founding Figure: Identify Gustav Fechner as a key early researcher who helped create the field of psychophysics.

  • Key Questions:

    • How well can we detect a stimulus?

• Absolute threshold

  • The minimum amount of energy or quantity required for a stimulus to be detected 50% of the time.

  • Measurement: It is measured by finding the point where you can detect the stimulus (e.g., sound volume) more than 50% of the time.

  • Absolute thresholds varies: 

• Among individuals (one person's threshold differs from another's).

• Across the lifespan (thresholds change as we age).

• Across species (e.g., a dog has a lower absolute threshold for sound than a human).

Significance: Having a lower absolute threshold means an organism is more sensitive to that specific stimulus (e.g., a cat has a lower absolute threshold for light, meaning it can detect weaker light/shadows).

• Difference threshold

  • The smallest difference in intensity required for a stimulus to be detected 50% of the time, dependent on initial stimulus intensity (Weber’s law).

  • Example: Adding salt to food until you can taste the change.

Just Noticeable Difference: This is the perceptible difference itself. The terms "difference threshold" and "just noticeable difference" are often used interchangeably to refer to this minimum detectable change.

2. The Role of Original Stimulus Intensity

The main factor influencing the JND is the intensity of the original stimulus:

• Rule: The more intense the original stimulus, the larger the change that must be added for the difference threshold to be reached (for you to notice the change).

• Example:

  • Adding 1 pinch of salt to 1 pinch is easily noticeable.

  • Adding 1 pinch of salt to 4 pinches is not likely to be noticeable.

Weber's Law 

• Formalizer: Ernst Weber (German physician, founder of psychophysics).

• The Law: Weber's Law states that the just noticeable difference (JND) between two stimuli changes as a proportion of those stimuli.

• The Concept: The amount of change needed to notice a difference is relative to the starting intensity, not absolute. The ratio between the JND and the initial stimulus intensity is constant.

• Example:

  • If you triple the size of a coffee (e.g., from 300 mL to 900 mL), you must also triple the amount of sugar (e.g., from 5g to 15g) for you to notice the change in sweetness.

  • Adding a constant amount of sugar (5g) to the large cup is less likely to be noticed than adding it to the small cup.

Limitation of Self-Report: The reliability of detecting a stimulus is based on self-report (what the individual says they sensed). This introduces an issue because people have different response biases (i.e., they aren't equally willing to report a weak stimulus).

Real-World Implications: This inconsistency has practical consequences, illustrated by the example of a radiologist who might miss tumors due to either a high absolute threshold or a low willingness to report what they're unsure of.

The Question Asked: The final question—"How do we confirm whether these stimuli were truly perceived or whether the individuals were just guessing?"—is the prompt that leads to the next concept (likely Signal Detection Theory), which is designed to solve this problem.

Examples of Absolute Thresholds

Adopted from Brown et al., 1962; D. Weston, 2003:

• Vision: A candle flame 30 miles away.

• Hearing: A watch ticking 20 feet away.

• Smell: A drop of perfume in a six-room house.

• Taste: A teaspoon of sugar in a gallon of water.

• Touch: A wing of a fly on your cheek, dropped 1 cm.

Signal Detection Theory: states that whether a stimulus is perceived depends on both the sensory experience and the judgment made by the subject.

• Decision-making occurs in the presence of uncertainty.

  • Stimulus Present / Absent:

  • Response Yes: Hit / False Alarm

  • Response No: Miss / Correct Rejection

Subliminal Processing (real but limited) 

• Subliminal Perception can, in fact, occur under strict laboratory conditions.

• The Myth vs. Reality: While self-help tapes are unlikely to work, the complete idea that all subliminal perception is a hoax is false.

• Effect: Subliminally presented stimuli can produce small effects in the nervous system and influence patterns of brain activity.

2. Priming Technique

• Method: The main laboratory technique used to study subliminal perception is priming.

• Priming Definition: Previous exposure to a stimulus influences an individual's later responses (to the same or a related stimulus).

• Laboratory Procedure:

  • A word or image is presented for a fraction of a second (the subliminal stimulus).

  • This is immediately followed by a mask (another image displayed for a longer time).

  • The mask interferes with conscious perception, meaning the person is often unaware the first stimulus appeared.

• Evidence: Despite the lack of conscious awareness, brain imaging studies show these rapidly presented stimuli do influence brain activity.

• Example Discussions:

  • "Sex sells?"

  • "Mind control?"

• Marketing Cases: References to LON GILBEYS LONDON DRY GIN and related campaign.

• Example: The Lion King movie promotions for IMAX theatres.

Gestalt Principles of Perception

Founder: Max Wertheimer (1910).

Key Observation/Illusion: While riding a train, he noticed that buildings in the distance appeared to be moving backwards (relative motion).

Laboratory Investigation: Using a stroboscope (a toy displaying rapid pictures), he discovered the central illusion:

• Individual images did not move.

• But when presented within a fraction of a second of each other, they created the perception of movement.

The Resulting School of Thought: This simple observation led directly to the development of Gestalt psychology. (The term "Gestalt" means "form" or "whole," reflecting the idea that the perceived whole is greater than the sum of its parts—i.e., multiple still images create the experience of movement).

Gestalt psychology: 

• an approach to perception that emphasizes that “the whole is greater than the sum of its parts.”

•  In other words, the individual parts of an image may have little meaning on their own, but when combined, the whole takes on a significant perceived form. 

• Gestalt psychologists identified several key principles to describe how we organize features that we perceive.

Figure-Ground Principle

• The Principle: The basic perceptual rule that objects or "figures" in our environment tend to stand out against a background ("ground").

• Visual Example: The text you read is the figure set against the white background.

• The Illusion: The principle is best seen when the distinction is ambiguous, as in the face–vase illusion . At the sensory level, there is only a pattern, but perception creates two objects with an ambiguity as to which is the figure and which is the ground.

• Auditory Example: When talking at a crowded party:

  • The voice you attend to is the figure.

  • The background noise is the ground.

• Dynamic Nature: Which object is the figure and which is the ground depends on factors like motivation and what you choose to pay attention to (e.g., if you switch attention from the person to the music, the music becomes the figure).

Additional Gestalt Principles

1. Proximity

   • The Principle: We tend to treat two or more objects that are in close physical proximity (near each other) as a single group.

   • Example: People standing close together in a photograph are perceptually assumed to be a single group.

2. Similarity

   • The Principle: We tend to group together individuals or objects that share visual similarity (e.g., color, shape, uniform).

   • Example: On a soccer field, players wearing the same uniform are grouped together as one team, separate from the other team based on their visual similarity.

Final Gestalt Principles

1. Continuity (Good Continuation)

   • The Principle: The perceptual rule that lines and other objects tend to be seen as continuous rather than abruptly changing direction.

   • Example: A winding object that passes behind another object is perceived as one continuous object, not two separate ones.

2. Closure

   • The Principle: The tendency to fill in gaps to complete a whole object. Our mind completes the incomplete forms to see a unified, whole image.

Overall Significance of Gestalt Psychology

• Core Message: The Gestalt principles (Figure-Ground, Proximity, Similarity, Continuity, and Closure) demonstrate a crucial characteristic of perception: We create our own organized perceptions out of the different sensory inputs we experience.

• Conclusion: Perception is not just passively receiving data; it is an active process where the observer (or "you") organizes and structures the sensory world.

Attention and Perception

1. Divided Attention

• Definition: The phenomenon of simultaneously paying attention to more than one stimulus or task at the same time.

• Examples: Playing a video game while talking; using social media while listening to a lecture; talking on a hands-free phone while driving.

• Consequence: Although we often feel we perform well, substantial evidence shows that dividing our attention negatively affects our performance.

2. Selective Attention

• Definition: Focusing on one particular event or task while minimizing attention to others.

• Examples: Focused studying, driving without distraction, attentively watching a movie.

• Benefit: Allows you to accurately sense and perceive the information provided by the focused task.

• Cost: Your perception of other parts of your environment suffers (e.g., you fail to notice background details or events).

• Extreme Case: The text hints that selective attention can be so powerful that we fail to perceive some very obvious things, setting up the next topic (likely inattentional blindness).

Human eye: 

• Senses array of information, translates that information into neural impulses and transfers it to the brain for complex perceptual processing 

• Key Structural Requirements: To perform its function correctly, the eye needs specialized structures to:

1. Regulate how much light enters.

2. Respond to different wavelengths of light (color).

3. Maintain a focus on objects in a scene.

4. Turn physical energy into action potentials (the method of information transmission in the brain).

The Structure of the Eye and Light Pathway

1. 

2. Focusing and Transduction

The Blind Spot 

What it is: The small area in the retina where the optic nerve exits the eye and connects to the brain.

Cause: This spot contains no photoreceptors (rods or cones).

Consequence: Because there are no light-detecting cells here, any light focused onto the blind spot cannot be transduced (turned into a neural signal), creating a physical gap in our visual field.

Perception: We don't usually notice the blind spot because the brain fills in the missing visual information based on what the other eye sees or the surrounding image.

Retinal Structure

• Components of the retina include:

  • Photoreceptors contributing to ganglion cell receptive fields.

  • Horizontal, bipolar, and amacrine cells process signals from photoreceptors.

  • The optic nerve conveys visual information to the brain.

  • Lateral geniculate nucleus (LGN) located in the thalamus processes visual information before it reaches the visual cortex.

How the Eye Gathers Light

1. Light and Its Function

• Primary Function of the Eye: To gather light and change it into an action potential.

• Definition of Light (for perception): Light is radiation that occupies a relatively narrow band of the electromagnetic spectrum.

2. Properties of Light Waves

Color Vision

• Key Aspects:

  • Wavelength (hue): Determines color perception.

  • Amplitude (brightness): Influences perceived intensity of light.

  • Purity (saturation): Indicates how much a color differs from white.

• Trichromatic Theory (Young-Helmholtz Theory):

  • Color perception occurs via three types of color receptors:

• Long wavelengths correspond to the perception of reddish colors.

• Short wavelengths correspond to the perception of bluish colors.

• In-between wavelengths (e.g., between red and blue) correspond to green shades.

• Afterimages can result from overstimulation of specific cones.

• Opponent-Process Theory:

  • Colors are perceived in terms of opposing pairs:

  • Red-green, yellow-blue, white-black.
    
    

3.Interspecies Differences

•  Visual system differences exist across species (e.g., bees see ultraviolet, reptiles see infrared).

• These differences are attributed to different evolutionary demands.

• Hypothesis for Human Vision: Some researchers suggest our red–green vision developed to distinguish between types of edible vegetation.

The Retina: From Light to Nerve Impulse

The Retina and the Perception of Colours

Key idea:
Colour is not a property of objects — it’s how our visual system interprets wavelengths of light.

• Cones in the retina respond to different wavelengths (short, medium, long).
  
  

• The brain creates the subjective experience of colour.
  
  

1. Trichromatic Theory (Young–Helmholtz Theory)

• Proposed by Thomas Young and Hermann von Helmholtz.
  
  

• Three types of cones:
  
  

  • Short → Blue
    
    

  • Medium → Green
    
    

  • Long → Red
    
    

• Colour perception = combination of activity across these cones.
  
  

  • Example: Red + Green stimulation → Yellow
    
    

  • Equal stimulation of all cones → White
    
    

• Supported by modern research measuring light absorption in cones.

2. Opponent-Process Theory (Ewald Hering, 19th c.)

• We perceive colour in opposing pairs:
  
  

  • Red ↔ Green
    
    

  • Blue ↔ Yellow
    
    

  • White ↔ Black
    
    

• Explains afterimages (e.g., stare at green → see red when you look away).
  
  

• Works through ganglion cell activity:
  
  

  • A cell excited by one colour is inhibited by its opposite.
    
    

  • When the stimulation stops, the inhibited cells “rebound” → you see the opposite colour.

3. How They Work Together (Complementary Theories)

• Trichromatic Theory → explains colour detection at the cone level (retina).
  
  

• Opponent-Process Theory → explains colour perception at the ganglion cell and brain level.
  
  

• Together, they explain how we perceive the full spectrum of colour.
  
  

Common Visual Disorders

Mechanism: One cone type (usually red or green) does not contain the correct protein.

Most Common: Difficulty distinguishing between red and green.

Cause: genetics.

LASIK Surgery

In LASIK surgery, surgeons create a small flap on the surface of the eye and then use a laser to alter the shape of the cornea. Approximately 90% of people experience perfect vision after the surgery, although they may need additional corrections (or glasses) as they age.

Visual Perception and the Brain

I. The Visual Pathway to the Cortex

The visual message (action potentials) follows a specific neural route to the brain:

Optic Nerve -  Optic Chiasm

Optic Chiasm - Thalamus

Thalamus (specifically the Lateral Geniculate Nucleus) - Visual Cortex

II. Crossing the Midline (Optic Chiasm) 🧠

The optic chiasm is the point at which the optic nerves cross at the midline of the brain.

Contralateral vs. Ipsilateral:

Contralateral: Fibres from the inside half of the retina (closest to the nose) cross over to the opposite side of the brain.

Ipsilateral: Fibres from the outside half of the retina (closest to the temples) travel to the same side of the brain.

Resulting Organization: The left half of your visual field is initially processed by the right hemisphere of your brain, and the right half of your visual field is initially processed by the left hemisphere.

Function: This organization increases the likelihood that some visual abilities will be preserved if a person's brain is damaged.

III. Initial Processing in the Brain

Thalamus: The nerve fibres first connect with the thalamus, which is the brain's "sensory relay station."

The Lateral Geniculate Nucleus within the thalamus is specialized for processing visual information.

Visual Cortex: The final destination for initial processing is the visual cortex, located in the occipital lobe.

Feature Detection Cells

Discovery: First discovered by David Hubel and Torsten Wiesel.

Function: These are specialized cells in the visual cortex that respond selectively to simple and specific aspects of a stimulus, such as angles and edges.

IV. Streams of Vision (Secondary Visual Cortex)

From the primary visual cortex, information is sent to the surrounding secondary visual cortex for further processing, which is divided into two streams:

Visual Processing Pathways

3. Pathway of visual information:

   • Optic nerve > optic chiasm > lateral geniculate nucleus (LGN, thalamus) > primary visual cortex (V1, occipital lobe).

4. Feature Detectors: Specialized cells that respond to specific visual stimuli.

5. Processing Pathways:

   • Dorsal pathway:

   • Function: Responsible for object location and spatial configurations (“where”).

   • Ventral pathway:

   • Function: Handles object perception and recognition (“what”).

Neural impulses leave the visual centres in the occipital lobe along two pathways. The ventral (bottom) stream extends to the temporal lobe and the dorsal (top) stream extends to the parietal lobe.

Illusory Perceptions

• Example:

  • Yorick's skull illusion demonstrated through locking gaze at a mark and then shifting visual focus.

Image Segmentation

• Two types of processing:

  • Bottom-up: Stimulus processing without prior knowledge.

  • Top-down: Prior knowledge influences perception.

• Gestalt Principles:

  • Explore how we perceive patterns and forms:

  • Figure-ground relationship, Convexity, Closure/symmetry, Similarity, Proximity, Good continuation.

The Ventral Stream

Supporting Evidence: Lesion Studies

1. Prosopagnosia (or face blindness)

• Cause: Lesions (damage) in the Ventral Stream, often involving the Fusiform Face Area (FFA).

• Result: Specific difficulty in recognizing faces, confirming the ventral stream's role in face perception.

Perceptual Constancy

Perceptual Constancy is the ability to perceive objects as having constant shape, size, and color despite the fact that the actual visual information reaching the retina is changing (due to changes in perspective, distance, or lighting).

Types of Perceptual Constancy

The visual system maintains constancy by making relative judgments about the object and its surroundings.

The Dorsal Stream of Vision ("Where" or "How" Pathway)

• Location and Path: Extends from the visual cortex in the occipital lobe upwards to the parietal lobe.

• Original Proposed Function (Mishkin & Ungerleider, 1982): Locates the object in space, leading to the nickname the "Where" pathway.

  • Contrast: The Ventral Stream is the "What" pathway (object recognition).

• Revised Function (Western University Researchers - Goodale & Milner): The function is more specific, allowing you to interact with the object and guiding action. This is why it is often referred to as the "How" or "Action" pathway.

  • Example: Effortlessly reaching out, grasping, and sipping a cup of coffee.

• Evidence for Function: Damage to the dorsal stream causes great difficulty performing actions that require visual guidance, such as reaching for objects.

2. Patient DF Case Study

• Cause: Occipitotemporal lesions (damage to the ventral stream).

• Result: Suffered severe object identification problems (couldn't identify objects).

• Key Findings (Contrasting Tasks):

  • Perceptual Matching & Discrimination Tasks: Performed poorly (consistent with ventral stream damage).

  • Action Tasks & Localization Tasks: Performed normally (relying on the intact dorsal stream).

Depth Perception

Depth Perception is the ability to gauge the distances between objects and determine their location relative to each other. This ability is critical for visually-guided actions (e.g., driving, walking).

I. Binocular Depth Cues (Both Eyes)

These cues are based on the differing perspectives of both eyes. Humans have fine-tuned 3D vision (stereoscopic vision) because our forward-facing eyes give us overlapping visual fields.

II. Monocular Depth Cues (One Eye)

These are distance cues that can be perceived with only one eye.

III. Pictorial Depth Cues (Used by Artists)

Artists use these monocular cues to transform a two-dimensional surface (a painting) into a three-dimensional perception.

Audition & Equilibrioception

Audition (Hearing)

1. Sound Waves and Eardrum

   • Sound waves vibrate the eardrum.

   • Key characteristics of sound:

     • Frequency (measured in Hertz, Hz): Determines pitch.

     • Amplitude (measured in Decibels, dB): Determines loudness.

2. Ossicles and Cochlea

   • Ossicles (small bones in the ear) flex the oval window to move fluid in the cochlea.

3. Hair Cells Activation

   • Hair cells located in the basilar membrane are activated by motion initiated by sound waves.

4. Auditory Pathway

   • Sound signal travels from cochlear nerve to the inferior colliculus (part of the midbrain), onward to the medial geniculate nucleus (MGN) in the thalamus, and finally to the primary auditory cortex (A1) situated in the temporal lobe.

Sound Pressure Levels and Effects

• Dangerous Sound Levels: We begin to feel pain at about $ext{125 dB}$.

• Sound Levels and Their Effects:

  • Jet engines (near): ext{140 dB} 

  • Rock concerts: ext{110-140 dB} 

  • Thunderclap (near): ext{120 dB} 

  • Power saw (chainsaw): ext{110 dB} 

  • Garbage truck/Cement mixer: ext{100 dB} 

  • Motorcycle (25 ft): ext{88 dB} 

  • Lawn mower: ext{85-90 dB} 

  • Regular exposure to sound over ext{100 dB} for more than one minute risks permanent hearing loss.

  • No more than 15 minutes of unprotected exposure is recommended for sounds between ext{90 dB}and ext{100 dB} 

  • Hearing damage begins at ext{85 dB} (after eight hours of exposure).

  • Comfortable hearing levels are under $$ ext{60 dB}

  • Examples of sounds at different dB levels:

    • Whisper: ext{30 dB} 

    • Rustling leaves: ext{20 dB} 

Cochlea Anatomy and Function

• Basilar Membrane:

  • Tonotopic organization exists where different regions of the basilar membrane respond to different frequencies of sound:

    • Apex: Regions responsive to low frequencies.

    • Middle: Regions responsive to mid frequencies (~3000 Hz).

    • Base: Regions responsive to high frequencies.

• Inner Ear Components:

  • Semicircular canals: Responsible for balance and detecting angular motion.

  • Cochlear duct, stria vascularis, and tectorial membrane support the function of hair cells and sound processing.

Theories of Pitch Perception

• Place Theory: Proposes that pitch is determined by the location of hair cell stimulation on the basilar membrane.

• Frequency Theory: Suggests that pitch is determined by the frequency of the basilar membrane's vibrations.

• Volley Principle: Neurons fire in alternating patterns to create a perception of pitch.

Primary Auditory Cortex

• Auditory cortex shows cortical tonotopy, where specific areas are responsible for processing different frequencies:

  • Regions for territorial frequencies such as 16000 Hz, 8000 Hz, 4000 Hz, and so forth.

  • Connections noted in auditory dorsal and ventral streams of processing.

Equilibrioception

1. Vestibular System and Balance

   • Consists of vestibular sacs (utricles and saccules) and semicircular canals (ampulla).

2. Pathways:

   • The signals travel from the vestibular ganglion (nerves) to vestibular nuclei located in the brainstem.

   • Associated with the insula and experiences of motion sickness.

Somatosensation, Gustation, & Olfaction

Somatosensation

1. Mechanoreceptors

   • Located under the skin, they detect pressure and vibration.

2. Neural Pathway:

   • Dorsal root nerves transmit signals from the spinal cord > brainstem > thalamus > primary somatosensory cortex (S1) located in the parietal lobe.

   • Somatotopic map: Represented by the sensory homunculus.

3. Pain Perception (Nociception):

   • Types of pain:

     • Sharp Pain: Thickly myelinated fibers, rapid firing.

     • Dull Pain: Unmyelinated fibers, slower firing.

   • Gate-Control Theory: Explains interaction between small and large nerve fibers in pain perception.

   • Types of sensations included: Light touch, general pressure, deep pressure, temperature.

Gustation

1. Tastants: Substances that stimulate taste cells located in taste buds.

2. Neural Pathway:

   • Signals from taste buds travel through cranial nerves to the brainstem > thalamus > primary gustatory cortex (located in the insula; temporal lobe).

   • Primary tastes identified: salty (NaCl), sweet, sour, bitter, umami.

Olfaction (Smell)

1. Odorants: Chemicals that enter the nasal cavity.

2. Pathway:

   • Odorants attach to bipolar neurons (olfactory receptors) in olfactory epithelium, then proceed to olfactory bulb > olfactory nerve > primary olfactory cortex.

   • Connection made to olfactory memories and their incredible emotional potency 

Lecture 7: Consciousness

Consciousness refers to a person’s subjective awareness, which includes:

• Thoughts
  
  

• Perceptions
  
  

• Experiences
  
  

• Self-awareness
  
  

It involves the brain’s interpretation of sensory information (perception) and awareness of those experiences.
Consciousness extends beyond perception—it also includes awareness of perceptual and internal states.

2. Wakefulness and Sleep (Section 5.1)

Spectrum of Consciousness

Consciousness can be mapped along two axes:

• Level of consciousness (wakefulness)
  
  

• Content of consciousness (awareness)
  
  

Conditions of consciousness:

• Fully awake and aware → Conscious
  
  

• Deep sleep, general anesthesia → Unconscious
  
  

• Intermediate states → Mind wandering, hypnosis, etc.
  
  

3. Biological Rhythms and Sleep

Sleep is a biological rhythm, a pattern that repeats cyclically.

Types of Biological Rhythms

• Infradian rhythms: Longer than one day (e.g., menstrual cycle, circannual rhythms).
  
  

• Ultradian rhythms: Shorter than one day (e.g., heart rate, hormonal cycles).
  
  

• Circadian rhythms: Approximately 24 hours (e.g., sleep-wake cycle, hunger, concentration).
  
  

Regulation of Sleep

• The suprachiasmatic nucleus (SCN) in the hypothalamus regulates sleep-wake cycles.
  
  

• Ganglion cells in the retina send light information to the SCN.
  
  

• The SCN influences the pineal gland, which regulates melatonin production.
  
  

4. Light, Sleep, and Melatonin

• Melatonin levels rise at night and fall during the day.
  
  

• Blue light exposure (from screens) suppresses melatonin, disrupting sleep.
  
  

• The hypothalamus manages biological rhythms and hormonal responses related to sleep.
  
  

5. Recommended Sleep and Consequences of Deprivation

Recommended sleep duration: 7–9 hours per night.

Chronic sleep deprivation is linked to:

• Cardiovascular issues
  
  

• Increased stress and anxiety
  
  

• Mental health decline
  
  

• Reduced physical performance
  
  

• Poor academic performance
  
  

• Dependence on caffeine/energy drinks
  
  

• Excessive smartphone use
  
  

Memory consolidation: Sleep is essential for learning and storing new information.

6. Stages of Sleep and EEG Patterns

Brain wave progression:
β (Beta, alert) → α (Alpha, relaxed) → θ (Theta, light sleep) → δ (Delta, deep sleep)

7. Theories on the Function of Sleep

1. Restore and Repair Hypothesis:
   
   

   • Sleep restores brain energy and clears metabolic waste (“brainwashing”).
     
     

2. Preserve and Protect Hypothesis:
   
   

   • Evolutionary purpose—conserves energy and keeps organisms safe at night.
     
     

Fun Fact:
Dolphins and some birds show unihemispheric sleep—one hemisphere sleeps while the other stays awake.

8. Dreams

Theories of Dreaming

1. Psychoanalytic Theory (Freud):
   
   

   • Manifest content: literal storyline.
     
     

   • Latent content: hidden symbolic meaning.
     
     

2. Problem-Solving Theory (Cartwright):
   
   

   • Dreams help process and solve waking-life problems.
     
     

3. Activation-Synthesis Hypothesis (Hobson & McCarley):
   
   

   • Dreams are the brain’s attempt to make sense of random neural activity.
     
     

9. Sleep Disorders

10. Sleep Displacement

• Jet lag or shift work disrupts circadian rhythm, causing cognitive and mood impairments.
  
  

11. Drugs and Consciousness

Psychopharmacology

Study of how drugs influence the nervous system and behavior.

Psychoactive drugs alter:

• Mood
  
  

• Cognition
  
  

• Behavior
  
  

12. Routes of Drug Administration

13. Mechanisms of Drug Action

• Agonists: Increase neurotransmission.
  
  

• Antagonists: Decrease neurotransmission.
  
  

• Tolerance: Decreased responsiveness with repeated use.
  
  

• Dependence: Can be physical or psychological.
  
  

14. Neurotransmitter Systems

Acetylcholine (ACh)

• Agonists: Choline-rich diet, black widow venom (↑ ACh release).
  
  

• Antagonists: Botulin toxin (blocks release), curare (blocks receptors).
  
  

• Nicotine: Stimulant acting as ACh agonist.
  
  

• Organophosphates & Physostigmine: Inhibit ACh breakdown.
  
  

GABA

• Agonists: Benzodiazepines, alcohol → Sedative effect.
  
  

Dopamine (DA)

• Agonists: Cocaine, amphetamines, methamphetamine → Stimulants.
  
  

Serotonin (5-HT)

• Agonists: LSD, psilocybin, mescaline, MDMA → Hallucinogens.
  
  

Glutamate (GLU)

• Antagonist: Ketamine → Hallucinogenic and dissociative effects.
  
  

Opioids

• Natural: Morphine, codeine
  
  

• Semi-synthetic: Heroin
  
  

• Synthetic: Fentanyl
  
  

• Antagonist: Naloxone (used for overdoses)
  
  

Cannabinoids

• Active compound: THC (psychoactive component of cannabis)
  
  

• Endogenous ligands: Anandamide, 2-AG → Act on cannabinoid receptors.
  
  

15. Alcohol Study (Herz et al., 2004)

Participants consumed alcohol daily for 13 weeks:

• Initial: 400 mL/day
  
  

• Over time: Decreased intoxication and blood alcohol levels
  
  

• Suggests development of tolerance.
  
  

16. Summary and Key Takeaways

• Consciousness is the foundation of awareness and perception.
  
  

• Sleep plays vital roles in memory, restoration, and emotional regulation.
  
  

• Dreams reflect cognitive and neural processes.
  
  

• Sleep disorders can impair health and cognition.
  
  

• Psychoactive drugs alter consciousness through effects on neurotransmitters.
  
  

• Understanding these mechanisms is crucial for studying behavior and mental processes