Human Senses Overview

Hearing and Sound

• Sound is caused by repetitive fluctuations in the pressure of a medium, such as air
• The difference between the peak and the baseline of a waveform is called amplitude, and relates to the intensity of the sound
• The distance from one peak to the next in a waveform is called wavelength
• Frequency is the number of complete waveforms/cycles that pass a given point in space every second and is described in units called Hertz

Taste and Swallowing

• Without a sense of taste it would be impossible to swallow food without choking

Pain

• The gate control theory suggests a functional ‘gate’ in the spinal cord can allow or block pain impulses from travelling to the brain

Proprioception: Our Sense of Body Position

• Proprioception is the sensory system that tells us about the location of our body and its movements
• The sense of equilibrium (vestibular sense) detects head movements and the body's position in space
• The vestibular sacs of the inner ear connect the semicircular canals and the cochlea, and help contribute to the body's sense of balance
• Otoliths are small crystals in the vestibular sacs that, when shifted by gravity, stimulate nerve cells that inform the brain of the position of the head
• Semicircular canals are fluid-filled tubes in the inner ear whose fluid stimulates nerve cells that tell the brain about head movements
• Kinaesthetic perception is the sense that tells us where the parts of our body are in respect to one another
• Proprioceptors are receptors in muscles and joints providing the brain with information about movement and body positions

Perception

• Perception is the process of interpreting sensory information, using past experience, knowledge and understanding to create meaningful experiences

Three Approaches to Perception

• The computational model focuses on how the nervous system translates sensory information into an experience of reality
• The constructivist approach focuses on the perceptual system using sensory information to construct an image of reality
• The ecological approach argues that humans and other species are so well adapted to their natural environment that many aspects of the world are perceived without requiring higher level analysis

Perceptual Organisation

• Perceptual organisation involves determining which stimuli belong together to form objects

Basic Processes in Perceptual Organisation

• Figure-ground discrimination is the ability to differentiate between foreground objects and the background
• Gestalt laws of grouping are principles that explain how we tend to group stimuli together:
  • Proximity: Closer objects are more likely to be perceived as belonging together
  • Similarity: Similar elements tend to be perceived as part of a group
  • Continuity: Continuous sensations are perceived as belonging together
  • Closure: We tend to fill in missing contours to form a complete object
  • Texture: Objects with similar textures are likely to be perceived as belonging together
  • Simplicity: We tend to group features of a stimulus in a way that provides the simplest interpretation of the world
  • Common fate: Objects moving in the same direction at the same speed, we tend to perceive them as belonging together

Senses and Incoming Stimuli

• All senses respond to incoming stimulus energy, encode it in the form of nerve cell activity, and send the coded information to the brain
• Transduction is the process of converting incoming energy into neural activity
• Neural receptors are specialised cells that detect certain forms of energy and transduce them into nerve cell activity; they are located where transduction occurs
• Sensory adaptation is the process by which responsiveness to an unchanging stimulus decreases over time

Sensory Information and the Brain

• Except for smell (which is processed in the olfactory bulb), all sensory information entering the brain passes through the thalamus, then is relayed to the appropriate sensory area of the cerebral cortex

Psychophysics

• Psychophysics focuses on the relationship between the physical characteristics of environmental stimuli and the psychological experiences those stimuli produce

Absolute Threshold

• The absolute threshold is the minimum amount of stimulus energy that can be detected 50% of the time

Subliminal and Supraliminal Stimulation

• Subliminal stimulation is stimulation that is too weak or brief to be perceived
• Supraliminal stimulation is stimulation that is strong enough to be consistently perceived

Topographical Representations

• Features near one another in the world stimulate neurons near one another in the brain

Sensitivity

• Sensitivity is the ability to detect a particular stimulus from a background of competing stimuli

Weber's Law

• Weber's law states that the smallest detectable difference in stimulus energy is a constant fraction of the intensity of the stimulus
• The smaller the constant "K" is, the more sensitive a sense is to stimulus differences

Magnitude Estimation, Fechner’s Law

• Constant increases in physical energy produce progressively smaller increases in perceived magnitude
• If just noticible differences get progressively larger as stimulus magnitude increases, then the amount of change in the stimulus required to double or triple its perceived intensity must get larger too

Sensory Systems

• Senses are systems that translate external information into neural activity
• Sensations are the messages from the senses that make up the raw information that affects behaviour and mental processes
• Neural receptors detect specific forms of energy and convert them into neural activity (transduction)
• Sensory adaption is the decrease in responsiveness to unchanging stimuli

Sensory Information Processing

• Signal detection theory is a mathematical model that explains how personal sensitivity and response bias combine to determine a decision about detecting a near-threshold stimulus
• Just-noticeable difference (JND) is the smallest difference between two stimuli that is detectable, and is defined by Weber's Law
• Magnitude estimation involves assessing the perceived intensity of a stimulus, which is related to actual strength, as defined by Fechner's Law

Vision

• The ability to see in very dim light depends on photoreceptors called rods
• Near-sightedness and far-sightedness occur when images are not focused on the eye's retina
• Color blindness results when cones in the retina lack one of the three kinds of color-sensitive photopigments

Additional Notes

• Humans rely heavily on touch, sight and hearing senses to understand the world.
• Each sense responds to a specific form of energy: vision responds to light, audition responds to sound, touch responds to pressure, and taste and smell respond to chemical stimuli.