psy 214 lecture 5 (09/19/2010) – (vision) dr. …rachtma8/psy214/files/ntc05-1.pdfpsy 214 lecture...

PSY 214 Lecture 5 (09/19/2010) – (Vision) Dr. Achtman

Written by:{Lindsay Robinson}, {[email protected]} of 5

Corrections: • No corrections needed Announcements: • After the completion of chapter 4 a movie will be shown • First test is October 3, 2011 • Dr. Achtman is available during her office hours • The test will include multiple choice and short answer questions Lecture Notes: Review

• Last class we began to study vision including parts of the eye such as the cornea, retina, fovea, and periphery.

• Today we added dark adaptation experiments to our list of differences between rods and cones.

Dark Adaptation Experiments

• The book defines Dark adaptation as the visual adaptation that occurs in the dark, during which the sensitivity to light increases. This increase in sensitivity is associated with regeneration of the rod and cone visual pigments.

• The book defines Dark adaptation curve as the function that traces the time course of the increase in visual sensitivity that occurs during dark adaptation.

PSY 214 Lecture 5

Topic: Introduction to Vision Chapter 3, pages 55-71

Three adaptation curves, See page 54 in textbook



• If you are out in the sun and go into a dark room, at first both your rod and cone vision will be poor. However after approximately five minutes your cone vision (what is in your focal point) is at its peak. After 20 minutes your rod vision will be at its peak point.

Spectral Sensitivity

• The top diagram represents the threshold curve, which shows how much energy is needed to detect different wavelength of the spectrum. For example it takes the least amount of energy(lowest threshold) to detect yellow light.

• The bottom diagram shows the spectral sensitivity curve. It is essentially saying the same thing as the top diagram however it clarifies that a lower threshold is equivalent to higher sensitivity.

• Blue light = short wavelengths • Red light = longer wavelengths

• Cones = sensitive to higher wavelengths • Rods = sensitive to smaller wavelengths

• The Purkinje shift is the tendency for the peak of sensitivity in the human eye to shift toward the blue end of the electromagnetic spectrum in low levels of light.

• When the two spectral sensitivity curves (one

for rods and one for cones) are compared, it can be noted that cones are more sensitive in the light and the rods are more sensitive in the dark.



The Retina

d

• Receptive Cells- Rods and cones located in the very back of the eye.

o 120 million rods, rods converge o 6 million cones, no convergence

High convergence – good sense Low convergence- details, two individual lights are recognized

• Horizontal cells- a neuron that transmits signals

laterally across the retina and synapse with receptor and bipolar cells. They are part of the middle layer.

• Bipolar Cells- a retinal neuron that receives inputs

from the visual receptors and sends signals to the retinal ganglion cells. They are part of the middle layer.

• Amacrine Cells- a neuron that transmits signals

laterally in the retina and synapse with bipolar cells and ganglion cells. They are part of the middle layer.

• Ganglion Cells- a neuron in the retina that receives

inputs from bipolar and amacrine cells. The axons of the ganglion cells travel out of the eye in the optic nerve.

o 1 million ganglion cells

Visual Demo: In class we looked at two different pictures of the same tiger and were instructed to look at different points on the picture of the tiger and determine if there were any differences between the two. As a class we determined that one is unable to notice differences if the difference does not occur at the point in which we are focusing on. Whether you see something in focus or not occurs in the eye, the brain is not involved.



Lateral Inhibition

• The textbook defines lateral inhibition as inhibition that is transmitted laterally across a nerve circuit. In the retina, lateral inhibition is transmitted by the horizontal and amacrine cells

• Cells that talk sideways! In the diagram, when only receptor A is stimulated, the

response recorded by an electrode on A increases However when A and B are stimulated by light, the

response is less frequent. o A + B fires less because inhibitory from

other light o A and B INHIBIT each other!

Mach Bands, The left side of one band (A) inhibits the right side of the band to its left (B), making the right side of B seem darker. The left side of B is lighter because it is receiving little to no inhibition.



For more information: • Here is a webpage that describes the retina at a level of understanding for a school age child.

The webpage can help make sense of difficult terms and functions of the retina. http://faculty.washington.edu/chudler/retina.html

• Here is a webpage that explains more about mach bands and other examples of lateral inhibition. http://www.nku.edu/~issues/illusions/MachBands.htm

Real-life example: • During the daytime, we as humans are most sensitive to items that are yellow such as yellow .

However as night falls upon us, items such as blue flowers and green grass stand out to our eyes more because we are more sensitive to blue and green at night.

psy 214 lecture 5 (09/19/2010) – (vision) dr. …rachtma8/psy214/files/ntc05-1.pdfpsy 214 lecture...

Documents