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Detail Lecture 02 - w/ pic

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University of Toronto Scarborough
Matthias Niemeier

Lecture 02 First Step in Vision Example of Short Answer Question: Which kinds of psychophysical methods exist? Mention at least four. Describe one of them in more detail. A: Method of constant stimuli, method of estimation, method of limit, method of adjustment. Method of constant stimuli where you have stimuli such as light with different intensity at fixed value. Randomly present the stimuli to the participant in repetitive manner by keep coming back to same intensity and asked them if they see it or not every time its shown. Through this data, for each level of intensity, could calculate probability of that person to yes, from which derive a curve with low intensity with low probability & high intensity with high probability. The curve is sigmoid function. Vision Retina (back of eye) first stage of vision processing Light Physics Light a electromagnetic wave; a stream of photons, tiny particles that each consist of one quantum of energy o It is little piece out of a vast spectrum of electromagnetic wave starting from long wavelength (TV signal) to visible light from red to blue to very short wavelength to human visible light is very short spectrum of light o the shorter the wave length, the more powerful the wave is o light doesnt actually have a colour, it is our brain that assigns it in physic colours dont exist colour is created by the visual system 5 ways of light can work: absorbed, diffracted, reflected, transmitted, or refracted: Absorbed: energy (e.g. light) is taken up by some substance and not transmitted at all st o E.g. room w dust room (light in) will be reduced in brightness as opposed to when it 1 enter that room o E.g. Light on surface especially black it will be observed o E.g. Filters also absorbed that picture of filter is red because it only lets out (transmit) light that has wavelength that we perceive as red light all other wavelength are reduced & probably not completely filtered out Could have filter that are blue etc. Diffracted: Not directly do w eye it is a common phenomenon w waves of all sorts (it doesnt need to be light for e.g. it could happen to waves in water as well) o It occurs when wave of some sorts encounters some kind of obstacles waves bent or having waves that are spread out o For e.g. when waves pass through narrow aperture Reflected Energy is somehow redirected its path when it strikes a surface usually back toward its point of origin o When light hits the desk for e.g. --. So light is absorbed & some is reflected it happens w glass surfaces, also happens w eye E.g. brown desk some brown (dark orange) wavelengths is reflected back thus, view the desk as brown Purkinje reflections (is used in Purkinje eye (movement) tracking system) these reflection arise from the differential optical surfaces of the eyes o E.g. outer surface & inner surface of cornea that makes already the 2 reflective surfaces In total 4 images from the cornea & lens behind them o These reflection from front looks like little spot depending what kind of light source you have st th in the pic 1 & 4 reflection comes from the same light source & the position of bw these two depends on eye position Could measure the position of lights spots in your camera and can determine the eye- position thus, determine where your eyes is looking at
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