Sensory and Perception 

Action Potentials

• Action potentials are all or nothing, so strong stimulus produces more action potentials NOT bigger ones.
• The neurotransmitters being released from the presynaptic neuron trigger the action potential in the post-synaptic neuron.

Sensory Processes

Sensation: the basic processes by which sensory organs and the nervous system respond to stimuli in the environment and the elementary psychological experiences that result from these processes.

Perception: the more complex organizing of sensory information within the brain and the meaningful interpretations extracted from it.

Physical stimulus: the matter of energy of the physical world that impinges on sense organs.

The Sensory System

Sensory receptors: specialized structures that respond to physical stimuli by producing electrical changes that can initiate neural impulses in sensory neurons

• Have their neural pathways in the brain
• Have their type of receptors

Sensory neurons: spec-lined neurons that carry information from sensory receptors into the central nervous system

Transduction and Coding

Sensory Transduction: when a receptor cell produces an electrical charge in response to physical stimulation.

• The process by which receptors in the eye respond to light, receptors in the ear respond to sound, etc.

Sensory Adaptation

Sensory adaptation: the change in sensitivity that occurs when a given set of sensory receptors and neurons is either strongly stimulated or relatively unstimulated for a length of time.

• Can be mediated by receptor cells or by the central nervous system
• Receptor potential and rate or action potentials are reduced
• Senses are much more responsive to charging than unchanging stimulation

Smell

The stimuli for smell are molecules that evaporate into the air, are taken into the nasal cavity, and then become dissolved in mucous guild covering that olfactory epithelium.

Olfactory epithelium: contains roughly 6 mil olfactory sensory neurons

• Each is sensitive and contains 5-20 hairlike cilia

Age:

• Smell declines with age; elderly complain of lost taste but is a loss of smell

Gender:

• Women are generally more sensitive to smell and become more sensitive to specific odors with increased exposure
• This applies to women in reproductive years, not pre-pubescent, or post-menopausal women

Mother-infant bonding: both mothers and newborns can identify each other based on smell alone

Choosing a genetically compatible mate: many species prefer a mate that smells most opposite of them

Pheromone: a chemical substance that is released by an animal, and acts on the members of its species to promote some specific behavioral or psychological response.

• Most mammals have a vomeronasal organ which contains receptor cells specialized for responding to pheromones
• Mixed findings on humans’ susceptibility to pheromones

Odorants: a substance giving off a smell, that can enter through the nostrils or the mouth.

Nasopharynx: opening in the back of the mouth which connects the nasal cavity

• Chewing and swallowing pushes odorants into the nasal cavity

Flavor: consists of true taste as well as smell. We experience flavor as coming only from our mouth

• Pinching nostrils and closing eyes will mostly make it nearly impossible to distinguish flavor in most foods

Taste

Anatomy and Physiology:

• 2/3 of taste buds are on the tongue and the rest are on the roof of the mouth and the throat

• Specialized taste receptor cells are on the taste buds

• Can trigger neural impulses in taste sensory neurons, which send input to the primary taste areas in the frontal lobe and other parts of the brain

• Six primary taste/receptor cells include; sweet, sour, fat, umami, bitter, and salty.

  Generally, pleasant and unpleasant tastes correlate to nutritional and non-nutritional foods for our ancestors living in more natural, non-sedentary, environments

• Salt balances bodily fluids, sugar provides energy, and protein builds tissues

• Decaying matter tastes sour, and plant and animal toxins taste bitter

• Women are more sensitive to bitter tastes in the first three months. During pregnancy, when the fetus is most vulnerable to poisons

• Children’s extra sensitivity may have helped early development

Pain

Somatosense: we experience pain coming from our bodies, not the world.

Nociceptors: free nerve endings of pain sensory neurons located in many parts of the body

Free nerve endings: sensitive nerve terminals throughout the body

C fibers and A-delta fibers: two types of pain sensory neurons mediate two different waves of pain

• Fast “first” pain travels along the myelinated A-delta fibers, and slow “second” pain travels along C fibers

  Brain areas for three components of pain experience:

• The sensory component which depends largely on the sotomasensory cortex

• The primary emotional and motivational component depends on the person’s limbic system

• The secondary emotional and motivating component is suffering that derives from the person’s worrying about the future or about the meaning of the pain

Walls Gate-Control Theory of Pain: Pain depends on the degree to which pain input can pass through a gate to the CNS that enters the brain stem

• Can be mediated by learned and unlearned stimulus information coming down from the brain to the brainstem
• Increased pain sensitivity after the injury occurs at the injury site as well as the CNS gate

Hearing

Outer Ear: receives and funnels sound waves towards the structure where transduction occurs

Pinna: a flap of skin and cartilage forming the visible portion of the ear

Pitch perception: the aspect of hearing that allows us to tell how high or low a given tone is

• High frequencies stimulate the proximal end of the basilar membrane
• Low frequencies stimulate the distal end

Conduction deafness: ossicles become rigid and cannot carry sounds inward from the tympanic membrane to the cochlea

• Conventional hearing aids can help

Vision

Receptors: 130 million photoreceptors embedded in your retina

• Converts light into neural activity

Rods: insensitive to color, mostly responsible for peripheral vision and mission at night

Cones: color sensitive, responsible for clear vision

• The light shines into the eye through the lens, the clear opening inside the iris

Psychophysics

Psychophysics: the study of relationships between physical characteristics stimuli and sensory experience produces by those stimuli

• Not interested in physiology

Absolute threshold: the faintest debatable stimulus of any type of stimulus

Difference threshold: the minimal difference in magnitude between two stimuli that are required for the person to detect them as different