I. Sensation Chapter 6

A. What Causes Sensory Experiences? Sensation is the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment. In English, the stimulation of sensory receptors and the transmission of sensory information to the central nervous system (spinal cord and brain)

Sensory receptors are located in sensory organs such as the eyes and ears.   All of our senses have 3 tasks: Receive sensory stimulation, often using specialized receptor cells Transform that stimulation into neural impulses Deliver the neural information to your brain

Each receptor cell responds to one particular form of energy   Light waves (vision) Vibration of air molecules (hearing)

When there is sufficient energy, the receptor cell “fires” and sends to the brain a coded signal that varies according to the characteristics of the stimulus. The specific sensation that is produced depends on how many neurons fire, which neurons fire, and how rapidly these neurons fire.

The process of converting one form of energy into another that your brain can use is called transduction. Each sensory experience—the color of a flower or the sound of a fire engine—is an illusion created in the brain by patterns of neural signals.

B. Sensory Thresholds To produce any sensation at all, the physical energy reaching a receptor cell must achieve a minimum intensity called the absolute threshold.

Absolute threshold is the minimum stimulation necessary to detect a particular light, sound, pressure, taste, or odor 50% of the time. Any stimulation below the absolute threshold will not be experienced. Ex---beeps when you go for a hearing test

Although there are differences among people, the absolute threshold for our senses is pretty low. Hearing: the tick of a watch from 20 feet in very quiet conditions Vision: a candle flame seen from 30 miles on a clear, dark night Smell: one drop of perfume diffused throughout a 3 room apartment Touch: the wing of a bee falling on the cheek from a height of 1cm

Under normal conditions, absolute thresholds vary according to the level and nature of ongoing sensory stimulation. Ex—threshold for the taste of salt is higher after you ate salted peanuts Ex—Your vision threshold is much higher on a sunny day than at midnight on a moonless night

In both cases, the threshold would rise because of sensory adaptation In both cases, the threshold would rise because of sensory adaptation. Sensory adaptation is diminished sensitivity as a consequence of constant stimulation. Adapting to people in a dark movie theatre

You go to your neighbors’ house, and you immediately smell a musty odor. You wonder how they can stand it, but within minutes you no longer notice it. When we are constantly exposed to a stimulus that doesn’t change, we become less aware of it because our nerve cells fire less frequently. This is why stinky or heavily perfumed people don’t notice their odor, because like us, they adapt to what’s constant and detect only change.

When confronted by a great deal of stimulation, our senses become much less sensitive and when the level of stimulation drops, our senses become more sensitive. You can hear the breathing of a sleeping baby in a quiet room, but if we were on a city street during rush hour, the noise would be deafening if our ears didn’t become less sensitive to stimulation. Adaptation lets us go from a dark room into bright sunshine without experiencing great pain

Imagine that you hear a sound Imagine that you hear a sound. How much stronger must the sound become before you notice that it has grown louder? The minimum difference a person can detect between any two stimuli 50% of the time is called the difference threshold.

Ex—adding 1lb to a 5 lb load will be noticed, but adding 1 lb to a 100lb load probably will not. A musician must detect minute discrepancies when tuning an instrument Parent’s must detect the sound of their own child’s voice among others

The difference threshold varies according to the strength or intensity of the original stimulus. The greater the stimulus, the greater the change necessary to produce a just noticeable difference.

C. Extrasensory Perception What about people who claim to have an unusual power of perception that goes beyond the normal senses (ESP)?

ESP can refer to a variety of phenomena, including:   Clairvoyance—awareness of an unknown object or event Telepathy—knowledge of someone else’s thoughts or feelings Precognition—foreknowledge of future events

Despite decades of research, experimentation has not yet provided clear scientific support for the existence of ESP