Psych 351 Perception Test 2 Study GuideObject Recognition- Object recognition – The act of extracting information from an image- Challenges to object recognitiono Clutter: When there is an overload of objects to recognizeo Variety: In our everyday environment the brain is faced with processing many different types of stimulio Variable views: The problem of being able to recognize things from different angles View Invariance – The ability of the visual system to identify objects no matter what size/angle/position they are in- Location invariance – The ability to identify identical objects in different parts of the visual fieldo Allowed by complex neurons- Size Invariance – The ability to identify identical images which are different sizeso Interaction between different levels of the visual system is important in producing size invariance- Angle invariance – The ability to recognize an object regardless of its angle- Heuristics – The rules of thumb that the visual system must use to process images o Heuristics describe how our visual systems works without explaining why it works that wayo Edge detection – Finding out where all the edges in an object are V2 cells notice when there is a border between two colors Uses information from V1 neurons to find out where the vertical lines are V4 neurons assist in identifying curveso Contrast enhancement – Enhances the contrast between colors, making it easier for the rest of the visual system to find edges between objects V4 neurons identify coloro Uniform regions – regions of an image where all the color and texture are the same This is the principle which camouflage takes advantage ofo Top-down information – All knowledge about the world that organisms gather by interacting with the world and being alive Embodied robotics – A type of ai which learns the same way as humans through interacting with the worldo Depth perception – Our understanding that the world is 3D V2 is involved in this processingo Interpolation – Filling in information that is missing from a raw image Eg: perceiving a soccer ball in grass as one full soccer ball even though the ball is partially covered by grass Makes use of the gestalt principles- Human electrophysiology – The summed recording of action potentials, summed from outside he heado Contrast to animal electrophysiology, where we just stick an electrode in the animal’s brain. The same fundamental signal is being measured Has the opposite set of strengths and weaknesses to fMRI Is very fast and can measure action potentials directly, but cannot identify where in the brain it is taking place Can track events in .5 millisecondso Event-related Potentials (ERPs)o Electroencephalogram (EEG) – The raw signal of electrophysiologyo ERP is the average of EEG segments which all constitute the response to an event of interesto Topographical map – map of how big the ERP is at a particular time across the whole heado ERP has discovered that we recognize objects in stages The EEG lines representing responses to different objects start to be different from each other at 120 milliseconds First positive (P1) – The bump in the waveform where the responses to faces, objects and words differs If people are shown pictures of faces, and images that have the same spatial frequency but are all mixed up there is no difference at P1 By about 100 ms the visual system has sorted out visual precepts by their spatial frequencies N170 – The response which differentiates faces from other types of objects and scrambled faces, it is called such because it is negative and peaks at around 170 ms N400 – The ERP response at around 400 ms which begins to discriminate familiar things from unfamiliar things- The strength of fMRI is its ability to tell where a cognitive process is taking placeo The weakness is that fMRI is very slowo It takes 2-3 seconds to change in response to an event This makes fMRI not very useful for studying object recognition- Color Vision- Light – the part of the electromagnetic spectrum that our rods and cones can absorb o We perceive difference in EM wavelengths as differences in color Blue is the shortest wavelength while red is the longesto Spectral Power distribution (SPD) – A plot which measures the Wavelength and intensity of light The SPD for incandescent lights is very similar to the sun, while it is very different from the sun for fluorescent bulbs, this is why fluorescent light is so harsh and incandescent feels more naturalo Monochromatic light – a light source which emits only 1 wavelengtho Most light we see is reflected off of another surface Different surfaces absorb and reflect different wavelengths of light Hue – is determined by the wavelength that bounces off of an object into our eyes Saturation – refers to how vivid or faded a color is Brightness – How much light there is- When a lot of light is being directed at an object we perceive that object as brighto Color solid – A 3 dimensional representation of all possible colors Hues change as it is rotated around Saturations change as we move from the inside of the circle to the outside Brightness changes as we move up and down the solid- Additive color mixture – The result of mixing lights of different coloro Pixel – A tiny element of light which combines with others to form imageso This type of color mixing only results from mixing light- Subtractive color – the subtraction of colors results in a final coloro Present in the mixture of substances eg: painto Blue paint looks blue because it absorbs all wavelengths that hit it except for the blue ones (and small amounts of green ones)o If yellow and blue paint are mixed then only the green light is reflected o Printers use subtractive color mixing- Pointillism – The artistic practice of painting in dots that when viewed from far away would form one image- Trichromatic – The type of vision we have due to having three types of coneso It is a compromise of the visual system, there are combinations of wavelengths that are different, but we see as the sameo Our visual system could overcome this by having more types of cones, butthat would mean we would have less of each type, reducing visual acuityo Metamers – Two sets of light that are composed of different wavelengths, but combine to make colors that we perceive as being the same Metamer experiment –