Sensation and Perception
When Helen Keller was 19 months old she lost the senses of sight and hearing. The only
senses that aided her were touch, smell, and taste.
Psychologists divide the way we experience the world into two distinct phases:
- Sensation: detect external stimuli; an elementary experience such as colour or
motion without the more complex perceptual experience of what is being seen or
what is moving; detection
- Perception: is the brain’s further processing of these detected signals; construction
of meaningful and useful information about a particular environment
What we sense is the result of how we perceive.
Stimuli must be coded to be understood by the brain.
Transduction: the translation of stimuli into chemical and electrical signals.
Most sensory information first goes to the thalamus, a structure in the middle of
the brain. Neurons in the thalamus send information to the cortex where
incoming neural impulses are interpreted as sight, smell, taste, sound or touch.
Each sense organ contains different types of receptor cells. Each type of receptor
is designed to detect different types of stimulus energy.
To function correctly, the brain needs qualitative and quantitative information
about a stimulus.
Psychophysics measures the relationship between stimuli and perception.
Psychophysics examines our psychological experiences of physical stimuli.
The absolute threshold is the minimum intensity of stimulation must occur before you
experience a sensation.
A difference threshold is just the noticeable difference between two stimuli.
Weber’s law: this law states that the just noticeable difference between two stimuli is
based on a proportion of the original stimulus rather than on a fixed amount of difference.
That is, the more intense the stimulus, the bigger the change needed for you to notice.
Classical psychophysics was based on the idea of a sensory threshold. Early psychophysics
had ignored the important variable of human judgement. This changed their methods of
testing absolute thresholds and came up with signal detection theory which states that
detecting a stimulus requires making a judgement about its presence or absence, based on a
subjective interpretation of ambiguous information.
Response bias refers to the participant’s tendency to report detecting signals in an
Sensory adaptation is a decrease in sensitivity to a constant level of stimulation.
In taste, taste buds detect chemicals. The job of gustation is to keep poisons out of our
digestive systems while allowing good food in. the taste receptors are apart of the taste buds. Different taste buds are spread relatively uniformly. Every taste is a mixture of five
basic qualities: sweet, sour, salty, bitter and umami. Umami arises from the detection of
an amino acid – glutamate which is a sodium salt in Glutamic acid, and as monosodium
glutamate or MSG. taste relies heavily on the sense of smell. Food’s texture also matters.
The same food can actually taste different, because the sensation associated with that food
differs in different people’s mouths. But cultural factors influence taste preferences as well.
These cultural influences on food preferences start in the womb.
In smell, the nasal cavity gathers odorants. Olfaction has the most direct route to the
brain. A warm, moist environment helps the odorant molecules come into contact with the
olfactory epithelium, a thin layer of tissue embedded with smell receptors which transmit
information to the olfactory bulb, the brain center for smell. The smell signals bypass the
thalamus and goes directly to the amygdala and cortex. Pheromones are chemicals
released by animals that trigger physiological or behavioural reactions in other animals.
These chemicals do not elicit smells, but are processed in a similar manner to the olfactory
stimuli. They play a major role in sexual signalling in many species. They might be an
explanation as to why menstrual cycles in women who live together tend to s