Chapter 3: Sensation and Perception

Sensation

The process of receiving stimulus energies from external environment and transforming them into neural energy.

Perception

The process of organizing and interpreting sensory info so that it makes sense. It develops our own personal interpretation of the world around us.

Bottom-Up Processing

A method of interpretation in which the sensory receptors register information and send it to the brain for interpretation. Making sense of information presented to you.

Top-Down Processing

It involves higher cognitive processing where the organism is able to sense what is happening and to apply that framework to information from the world. An example is knowing the words to a song that is being played or even just thinking about the song.

Sensory Receptors

Specialized cells that detect stimulus info and transmit it to sensory nerves and the brain. Since neurons follow the all-or-nothing principle, they can only indicate the intensity of stimuli through increased frequency of action potential.

Types of Receptor Cells

• Photoreception: Detection of light perceived as sight

• Mechanoreception: Detection of pressure, vibration and sound perceived as touch, hearing, and equilibrium

• Chemoreception: Detection of chemical stimuli perceived as smell and tasteThermoreception: Detection of temperature changes perceived as warmth or cold.

Synesthesia

A condition in which in onset of induces experience in another sense, seeing colors in music.

Absolute Threshold

The minimum amount of stimulus that one person can detect 50% of the time.

Thresholds of the 5 Senses

• Vision: Candle flame 30 miles away on clear, dark night

• Hearing: ticking clock 20 ft away when quiet

• Smell: One drop of perfume diffused in three rooms

• Taste: tsp of sugar in 2 gallons of water

• Touch: wing of fly falling on your neck from distance of 1 cm

Noise

Irrelevant or competing stimuli.

Difference Threshold

The smallest difference between stimuli required to be noticed 50% of the time.

Webers Threshold

Discovered by E. H. Weber, it is a principle in which two stimuli must differentiate by a constant proportion to be noticed as different.

Subliminal Perception

The detection of stimuli below the level of conscious awareness.

SIgnal Detection Theory

A theory that explains how we detect signals amid noise, emphasizing the role of decision-making in perception. The detection of signals is based upon more than senses like fatigue, expectations, and the urgency of the moment.

Selective Attention

The art of focusing on a specific aspect of experience while ignoring others, but it can shiftable.

Cocktail Party Effect

The act of focusing upon one voice among a crowd of voices.

Novel Stimuli

New, different, or unusual stimuli. This often shifts our attention.

Inattentional Blindness

The failure to detect unexpected events when attention is engaged by a task. More likely to occur when a task is difficult.

Perceptual Set

A mental predisposition or readiness to perceive something in a particular way, which reflect top-down influences on perception. An example is noting less ace of spades due to some of them being red instead of black.

Sensory Adapation

A change in responsiveness of the sensory system based on the average level of surrounding stimulation. An example is vision readjustment after turning off the lights.

Amplitude

The height of light waves which determines the brightness of the stimulus.

Purity

The quality of light waves, either a mix or all the same, that determines the saturation or richness of a color.

Structures of the Eye

• Sclera: White outer part of the eye that helps maintain the shape of eye and protect from injury.

• Iris: Colored and contains muscles that control the size of the pupil. Acts like aperture of a camera.

• Pupil: Opening in the eye

Cornea and Lens

The cornea is a clear membrane at the from of the eye. First structure for focus.

The Lens transparent and flexible disk structure, gelatin-like material.

Curved surface of the cornea achieves most bending of light for focus. Bending more light needed for closer objects.

Retina

Acting as the eye’s “film”, it is a light-sensitive surface that records electromagnetic energy and converts it to neural impulses. Consisting of 126 million receptor cells that are rods or cones.

Rods and Cones

• Rods are sensitive to light but not useful for color vision. Great functioning when there is little light. 120 million in humans.

• Cones are receptors for color perception but need a larger amount of light to respond; so like daylight. 6 million cone cells in humans.

Fovea

The most important part of the retina, it is a tiny are in center of retina at which vision sees best. Only contains cones.

Optic Nerve

A bundle of axons of ganglion cells that carry visual information to the brain for further processing.

Blind Spot

The area in which the optic nerve leaves the eye on its way to the brain, nothing can be seen within this part of the retina.

Optic Chiasm

The point where the optic nerves from both eyes cross, allowing visual information from both eyes to be processed together in the brain. Left side of visual field is registered in right side of brain while right side of visual field is registered in the left side of the brain. Processed in the visual cortex.

Visual Cortex

Located in the occipital lobe, most visual information passes through before going to more analytical areas.

Feature Detectors

Specialized neurons that pick up specific features like edges, shapes, colors, and contours. Hubel and Wiesel recorded a single neuron of a cat and displayed various images.

Parallel Processing

The ability to have information travel quickly through the brain due to simultaneous distribution of info across different areas of the brain. This allows for the simultaneous processing of multiple aspects of a visual scene, such as color, motion, and form.

Binding

The process in which all the various neurons processing and analyzing information join together and integrate a complete interpretation of the information.

Trichromatic Theory

Proposed by Thomas Young, is a theory that suggests that color is perceived through three types of cone receptors with different, but overlapping ranges of wavelengths, red, green and blue.

Studying color blindness provides further proof since one, or more, of the three colors is impaired.

Ewald Hering

A physiologist that noted that some colors cannot exist together; you can image blue and green, but not red and green.Trichromatic images cannot explain afterimages.

Afterimages

Sensations that remain after a stimulus is removed; green afterimage after looking at red.

Opponent-Process Theory

The idea that there are actually four receptor cones that are organized into pairs: red-green and blue-yellow. After looking at a red stimulus, the red-green system may tire and thus cause you to see a green afterimage.

Figure-Ground Relationship

The perceptual organization of visual scenes where an object (the figure) is distinguished from its background (the ground), allowing us to focus on the main subject. This can be difficult to differentiate sometimes as pictures can, for example, show either seeing two faces or a goblet.

Gestalt Psychology

A school of thought that probes how people naturally organize their perceptions. They often view that the whole is different from its parts. Principles include:

• Closure: Disconnected/incomplete figures will have spaces between them filled.

• Proximity: groups objects are seen as a unit.

  • Similarity: Similar objects together are seen as a single unit.

Binocular Cues

Depth cues that are dependent upon the visual info from the left and right eyes that work together to perceive depth. These cues include convergence and retinal disparity, which help in judging distances and depth perception.

Disparity

The difference in the images seen by each eye, which helps the brain calculate depth and distance.

Convergence

A binocular cue that utilize eye muscles to determine depth/distance.

Types of Monocular Cues

1. Familiar Size and relative size:

2. Height in the field of view: higher objects are seen as farther away.

3. Linear perspective: Smaller objects are perceived as farther away.

4. Overlap: An object that conceals/overlaps another is closer.

5. Shading:

6. Texture gradient: Texture becomes denser and finer the farther the viewer is.

Apparent Movement

The perception that a stationary object is moving.

Perceptual Constancy

The recognition that objects are constant and unchanging even though sensory input shows them as changing. There are three types:

• Size constancy

• Shape constancy (table is still same even if you walk around it)

• Color constancy

Frequency

The number of cycles that pass within a certain interval

Pitch

The perceptual experience of a frequency; high frequency is high pitch.

Amplitude

The amount of pressure the sound wave produces relative to a standard; decibels.

Loudness

The perception of the sound wave’s amplitude.

Timbre

The tone saturation or perceptual quality.

Pinna

A part of the outer ear, it connects to the external auditory canal, and it serves collect sounds and channel them into the ear canal.

Parts of the Middle Ear

• Eardrum (Tympanic Membrane): a membrane that separates the outer and middle ear and vibrates in response to sound.

• Hammer, Anvil, and Stirrup: An intricate chain of bones, ossicles, that vibrate and transmit sound waves to the fluid-filled inner ear.

Parts of the Inner Ear

The inner ear serves as converting sound waves into neural impulses.

• Oval Window: A membrane-covered opening that leads from middle ear to inner ear.

• Cochlea: Transmitted from the oval window, it is a tubular, fluid-filled structure that is coiled.

• Basilar Membrane: lining the inner wall of the cochlea, it is narrow and rigid at the base but widens and becomes more flexible at the top. Width variation allowed different area to vibrate with different intensities for different sounds.

• Hair Cells: they have cilia sprout from them. Movement against the tectorial membrane, jellylike flap, generates impulses that are computed a sound. Cannot regenerate.The inner ear includes structures such as the cochlea, which converts sound waves into neural impulses, and the vestibular system, which aids in balance.

Cochlear Implants

A small device surgically implanted in the ear that allow the auditory-impaired to detect sound. Not a hearing aid since they amplify sounds.

Place Theory

The theory in which each frequency produces vibrations at a particular place on the basilar membrane. Von Békésy studied the effects of frequencies on the basilar membrane. High-frequency vibrations create traveling waves that maximally displace the areas of membrane closer to oval window. Low frequencies go closer to the tip of the cochlea. Works best for high-frequency sounds, but low frequencies displace larger areas, which make identification of exact location difficult.

Frequency Theory

The theory that suggests that the perception of a sound’s frequency is based upon how often the auditory nerves fire. A limitation is that neurons are limited to firing 1,000 times a second, so it cannot be applied to frequencies that require more rapid firing.

Volley Principle

Developed to deal with the limitation in frequency theory, it states that neurons can team up to alternate neural firings to attain a higher rate for the frequency.

Auditory Nerve

Nerve structure that receives info about sound from hair cells of inner ear and carries to brains auditory areas.

How is Sound Localized?

The sound coming from a direction has two different distances to travel to reach each ear. Additionally, the sound shadow also reduces the intensity of the sound.

Cutaneous Senses

touch, temperature, and pain

How Touch is Transported to the Brain

Sensory fibers arising from receptors in the skin enter the spinal cord. Fibers from each side of the body cross over to opposite sides of the brain. Information about touch moves on to thalamus which projects map of body’s surface onto somatosensory areas of the parietal lobes in cerebral cortex.

Thermoreceptors

sensory receptors that detect temperature in order to maintain body temp; divided into cold and hot sensors. Warm and cold receptors close to each simultaneously stimulated experience a hotness sensation.

Pain Receptors

Some respond to pressure, others to heat, some both, but many are chemically sensitive to a range of pain-producing substances.Inflamed joints or sore, torn muscles produce prostaglandins, fatty acids that stimulate receptors to experience pain. Fast pathways connect directly to thalamus and the to motor and sensory areas; it serves as a warning system of danger and takes less than second. Slow pathway: pain travels through limbic system, slower, and seems to serve as means of reminding injury and to tell the body to let it heal. Neuroscientists believe that brain generates experience of pain since it produces endorphins.

Papillae

They are taste buds, amounting to 10,000, replaced every 2 weeks. They include many tastes beyond sour, sweet, spicy, and salty. Looking into umami which means delicious and refers to the flavor of L-glutamate.

Olfactory Epithelium

The lining of the roof of the nasal cavity, containing a sheet of receptor cells for smell. They attached with millions of hairlike antennae; can be replaced after injury. The neural pathway for smell passes right to the olfactory areas in the temporal lobes. It then takes superhighway to emotion and memory.

Kinesthetic Senses

Provide info about movement, posture, and orientation. Contaib=ned within the muscle fibers and joints.

Kinesthesia

The name for kinesthetic senses and is not noticeable.

Vestibular Senses

Provides info about balance and movement. Tells us whether our head is tilted, moving, slowing down, or speeding up.

Proprioceptive Feedback

Info about the position of our limbs and body parts in relation to other body parts.

Semicircle Canals

Within the inner ear, they contain sensory receptors to detect head motion. They consist of three fluid-filled, circular tubes that lie in three planes of the body.

Proprioceptive Drift

Refers to the perception that something other than our actual body belongs to us and is part of our body.