Introduction to Perception: Visual Perception

Aim: When we look at the world, why does it seem stable or constant? Do Now: Describe this image.

Perception: The process of assembling and organizing sensory information to make it meaningful.

Illusions: Inaccurate perceptions

Definitions Distal stimulus: The actual stimulus (e.g., object, sound) that exists in the environment Proximal stimulus: The information that registers on your sensory receptors (e.g, the image of the object on your retina) Iconic memory: Visual sensory memory that allows a proximal stimulus to persist for 200-400 ms. after the stimulus has disappeared Thinking about the information processing model, how do we interpret stimuli that enter into our senses?

Why does line (a) in the Muller-Lyer illusion look longer than line (b)?

Gestalt: An organized whole, shape or form Gestalt: An organized whole, shape or form. Similarity: A perceptual cue that involves grouping like things together. Proximity: A perceptual cure that involves grouping thing that are near one another.

Closure: The process of filling in the missing details of what is viewed.

Although there are no lines indicating a square, our visual system imposes a square on these shapes.

Illusory Contour Illusion We see contours even when they are not present in the stimulus Some cells in our visual respond to the contours formed by the triangles The visual system unifies the stimuli into the perception of a square

Monster Size Illusion The upper right creature looks larger than the lower left If you measure them, they are the same size Depth perception: cues in the background, such as converging lines, contribute to a perception of distance This is a constructive activity of your brain.

The Visual Cliff: Used to demonstrate depth perception

Gestalt: humans have basic tendencies to organize what they see Gestalt: humans have basic tendencies to organize what they see. It’s ambiguous because you have mental representations for both the faces and the goblet. Even in ambiguous situations, our perceptual system imposes organization on a stimulus so that a portion stands out (becomes the figure) and the rest recedes into the background

Figure Ground (Ambiguous Figure) Illusion Figure = distinct shape with clear edges Ground = left over region Figure seems closer to us and more dominant In ambiguous figures, figure and ground reverse, because we can recognize both representations

Do you see an old woman or a young woman in this illustration      Do you see an old woman or a young woman in this illustration? They are both present, but you will not be able to see both of them simultaneously. Once you perceive both figures, see if you can get them to fluctuate back and forth between the two interpretations. What's Going on Here?      This type of reversible figure concerns the meaningful content of what is interpreted by your brain from the same static image. Your perception of each figure tends to remain stable until you attend to different regions or contours. Certain regions and contours tend to favor one perception, others the alternative. Even though certain contours in this figure are ambiguous, your perceptual change in this case does not involve a figure/ground reversal.      When the provocatively turned cheek becomes the cheek-nose, the rest of face abruptly changes following the lead of the nose. For example, if a certain line is tentatively identified as a nose, then the line below it must be the mouth and the shapes above it must be the eyes. These partial identifications mutually support one another to form a stable perception. The identifications of wholes and of parts will likewise be recprocally supportive, contributing further to the locking-in process.  Your visual system tends to group like or related regions together. It does not present you with some odd mixture of the two alternatives.      Attending to different regions or contours does tend to initiate a change of perception. However, it is not necessary to shift your gaze for a perceptual change to occur. It can be entirely spontaneous. If this image is looked at with a steady eye, it will still change, though less often.  Researchers have stablized the image directly onto the retina to eliminate  any effects that may arise from eye movements. Even uder these conditions, a perceptual reversal may occur. This indicates that higher cortical processing occurs that strives to make meaning out of a stable image presented to the retina. This illustrates once more that vision is an active process that attempts to make sense of incoming information. As the late David Marr said, "Perception is the construction of a description."

Old Woman/Young Woman Face perception Why study face recognition? Agnosia is an impairment in visual object recognition. Proposagnosia is an impairment in visually recognizing faces. Visual agnosia is an inability to recognize visual objects that is neither a function or general intellectual loss nor a loss of basic sensory abilities Under Visual Agnosia: 1/ apperceptive agnosia (early perceptual processes are disrupted) & associative agnosia (later processes (pattern recognition) are disrupted

How do we assign meaning to stimuli? F Letters Objects Faces

Inattentional Blindness Also known as "perceptual blindness" which is the phenomenon of not being able to see things that are actually there. This can be a result of having no internal frame of reference to perceive the unseen objects, or it can be the result of the mental focus or attention which cause mental distractions. The phenomenon is due to how our minds see and process information.