Perceptual Development (Sensation and Perception)
Rely heavily on visual. Incoming sensory input human rely on, not so much other species.
Second most important is auditory. Oldest, evolved first is olfactory. Fourth-gustatory-taste. Last
one touch-different receptors: pain, heat, pressure, vibration. Other: vestibular (balance) system.
Principles of Sensation: to transduce incoming information into a neural signal. Ie/sensory
memory. Registering all 5 modalities into a meaningful thought-complex process.
• Transduction- physical energy to neural signal
• Absolute threshold-smallest strength of a stimulus that can be detected. Sensory detectors
are really sensitive. Detect differences in color, detect things far away and sounds.
• Difference threshold- jnd- smallest difference that can be detected. Primary
somatosensory cortex- touch.
• Sensory adaptation- use sensation to adapt to environment.
Infants are born legally blind. Sense adults rely on and least well developed at infancy.Auditory
well developed at birth.
Vision-relied most on
Purpose: transform light energy into an electrochemical neural response. Represent
characteristics of objects in our environment such as size, color, shape and location.
Incoming input is electromagnetic radiation-energy that occurs in a spectrum, occurring in waves
of energy. Energy and mass interchangeable. Frequency-length of a wave. Visual part of
spectrum being detected 400-700nm. Spectrum-radio waves. Gamma and x rays get in between
molecules, inside human and gamma can disrupt organs (radiation poisoning) because gamma
rays are very short. Radio waves are too large and cant hurt you. Electricity has largest frequency
with electromagnetic radiation. Cant hurt you or cancer because waves are too long and cant get
inside of you.
Frequency/wavelength determines colour.Amplitude- how high the waves are, can be tall or
short, determines the brightness. First thing infant is able to detect is contrast-the brightness of an
There are different receptors that detect color and brightness. Magnocelluar system-color and
parvocellular system-contrast put together in the occipital lobe separately. Detection of
Movement shape and location is a different system.
Very short: gamma rays. Very large:AC circuits-electricity. Color: 400-750. smallest violet,
largest red. Radar- microwaves- can hurt, long wavelengths.
Light: The Visual System
• Light can be described as both a particle and a wave.
• Wavelength of a light is the distance of one complete cycle of the wave. Also referred to
frequency- number of waves that occur per second, hertz.
• Visible light has wavelength from about 400nm to 700nm.
• Wavelength of light is related to its perceived color. Infants are perceiving contrast at low
quality. -incoming electromagnetic radiation detected by a camera, outer protective layer. transparent:
cornea. Behind is lens-to focus, lens bends light to accommodate (accommodation, in camera is
called focus) distance by muscles that change the shape. Lens accommodation in infancy not
very good focus. If cant accommodate, need glasses as a second lens. Iris is color-if no color,
albino-pink is no color. Most common-brown, least-green. Your eyes can accommodate for too
much information-develops within the first three months of life. Middle of iris is pupil-not a
structure (black dot). Iris is attached to muscles which makes pupil dilate or contrast. Too bright-
pupil shrinks, dark- pupil dilates. Dark, pupil opens to let more light in. Pupil is an opening so
black. Accommodate amplitude bright and distance. Incoming electromagnetic radiation
accommodating for distance and brightness.
-transduction takes place at the back of the eyeball-well developed in infancy but not working
well. Retina- back of the eyeball, consists of receptors of electromagnetic radiation.
Optic disc: point where optic nerve eaves eye; no rods or cones in this part of retina creating a
blind spot, filled in cognitively by cortex.
Retina has 3 layers of receptors at the back of the eyeball: sensory receptor cells-detecting
contrast by rod/ color by cones sensitive to wavelengths. Two different parts of visual system.
Rods form earlier-contrast develops early. Cones are organized in fovea. Specialized for
detecting color. Fovea: point of highest visual acuity, cones concentrated here. In periphery have
rods for movement/contrast. Next layer-bipolar cells: coordinating information from receptors
(rod and cones). Rods connected to multi-bipolar neurons, cones connected to single bipolar
neuron- produce acuity. Bipolar cells then connected to ganglion cells. Optic nerve fibers: axons
of ganglion cells form fibers of optic nerve.
Cones: allows us to see in bright light, fine spatial detail and be able to see different colors.
Rods- allow us to see in dim light, cannot see fine spatial detail or cannot see different colors.
Which one sensitive to electromagnetic radiation of color-rods or cones?A: rods. Very sensitive,
cones need bright lights. In dim, can still see objects. Cones require a lot of radiation to see. Rods
have low acuity but very sensitive, can still see things in the dark. Reason why rods develop
earlier then cones.
• Ganglion ce