Gestalt Principles of Perception Psychology 355: Cognitive Psychology Instructor: John Miyamoto 04/08 /2015: Lecture 02-3 This Powerpoint presentation may contain macros that were used to create the slides. The macros aren’t needed to view the slides. If necessary, you can disable the macros without any change to the presentation.

Outline Gestalt Principles of Perception Lateral inhibition & feature representations in perception Phenomenological evidence for motion detectors in vision Psych 355, Miyamoto, Spr '15 2 #

Inverse Projection Problem Psych 355, Miyamoto, Spr '15 3 Inverse Project Problem: For any 2-dimensional image that is projected onto the retina, there are infinitely many different 3-dimensional shapes that could have produced that image. How does the mind decide which shape actually produced the 2-dimensional projected image? Ambiguous Figures: The Ambiguous Box Slide repeated from yesterday

Gestalt Principle of Similarity Similar things are grouped together. Similarity in lightness, shape, color, size, and orientation cause grouping. a a a a a a aa b c d e f g b b b b b b b a b c d e f g c c c c c c ca b c d e f g d d d d d d da b c d e f g e e e e e e ea b c d e f g f f f f f f fa b c d e f g g g g g g g ga b c d e f g (looks like rows)(looks like columns) Psych 355, Miyamoto, Spr '15 4 Principle of Good Continuation Slide repeated from yesterday

Gestalt Principle of Good Continuation Connected points result in smoothly curving lines. Points are seen as they belong together. Lines follows smooth path. Psych 355, Miyamoto, Spr '15 5 Figure-Ground Principle Slide repeated from yesterday

Figure-Ground Principle and the Principle of Smallness Figure/ground Principle – ambiguous figure The famous faces/vase figure. Psych 355, Miyamoto, Spr '15 6 Escher Print #1 Principle of Smallness implies that we should see vases on the left and faces on the right Face is Face is background foreground Slide repeated from yesterday

Figure-Ground Example Downloaded from ery/A41L.html ery/A41L.html Maurits Cornelis Escher Dutch graphics artist Figure-ground problem: Separation of object from background Psych 355, Miyamoto, Spr '15 7 Escher Print #2 Slide repeated from yesterday

Another Figure-Ground Example Downloaded from Psych 355, Miyamoto, Spr '15 8 Principle of Common Fate Slide repeated from yesterday

Gestalt Principle: Common Fate Principle of common fate: Things that are moving in the same direction (at the same speed) appear to be grouped together. Go to website – look at it: This is a nice demonstration of the common fate principle. The groups of lines or shapes are only visible as a group when they are moving together. ♦ WARNING: The preceding demonstration requires a browser that has JAVA activated. I don’t understand the technicalities, but there are dangers (computer viruses) associated with the use of JAVA. If preceding example is not available, try : Kinetic depth effect Psych 355, Miyamoto, Spr '15 9 9

Goldstein Figure 3.21: Gestalt Principles Can Trick the Eye What Gestalt principles are used here to create the illusion of a semi-transparent woman? Principle of Good Continuation Principle of Similarity Psych 355, Miyamoto, Spr '15 10 Figure 3.21 Waves by Wilma Hurskainen Same Slide - No Arrows or Extra Lines

Goldstein Figure 3.21 What Gestalt principles are used here to create the illusion of a semi-transparent woman? Principle of Good Continuation Principle of Similarity Psych 355, Miyamoto, Spr '15 11 Figure 3.21 Waves by Wilma Hurskainen Examples of Gestalt Principle in Visual Design

Examples of Gestalt Principles in the World of Visual Design Psych 355, Miyamoto, Spr '15 12 Principle of similarity implies that we see the three left figures as a group. Thus the right figure is an exception (anomaly) so it stands out. Principle of Figure/Ground Principle of Good Continuation: We "see" the motion of the leaf. Principle of Simplicity Summary: Evidence for Gestalt Principle of Perception

Summary – Evidence for Gestalt Principles of Perception Phenomenological support Experimental evidence – image segmentation (Not discussed in this lecture) Gestalt laws are perceptual heuristics Gestalt laws help to explain how the visual system solves the inverse projection problem (inferring a specific reality from ambiguous inputs). Important in the theory of object perception Psych 355, Miyamoto, Spr '15 13 Examples of Visual Feature Detectors

Psych 355, Section, Spr '15 14 Examples of Visual Feature Detectors Hubel & Wiesel used single-cell recordings to demonstrate the existence of feature detectors in the visual system. Lots of evidence for feature detectors: ♦ Single-cell recordings ♦ Visual illusions that can be explained by lateral inhibition (inhibition of neighboring neurons) ♦ fMRI evidence (not discussed in this lecture) Many different types of neural feature detectors have been found: edge and bar detectors, motion detectors, texture detectors, color detectors, etc. Important Hypothesis: Many perceptual and cognitive processes are based on feature representations. Lateral Inhibition

Psych 355, Section, Spr '15 15 Lateral Inhibition Cells that are ON-center/OFF surround inhibit activity of adjacent cells when the center is stimulated. Lateral inhibition refers to the effects of inhibition on adjacent neurons, especially when the inhibition enhances the perception of edges, bars or other patterns. Lateral Inhibition Plays a Role in Edge & Bar Detectors

Psych 355, Miyamoto, Spr '15 16 Hermann Grid Stare at the grid. What do you see? Apply Idea of Lateral Inhibition to Construction of Edge & Bar Detectors

Psych 355, Miyamoto, Spr '15 17 Two Perceptual Phenomena with the Hermann Grid 1)Phantom dark spots appear at the intersections of the white lines. 2)The dark spots disappear when you look directly at them. Why? Use Lateral Inhibition to Explain the Perception of the Hermann Grid

Hermann Grid Illusion is Due to Lateral Inhibition? Psych 355, Miyamoto, Spr '15 18 We see phantom dark spots at the intersections to the side of the focus of vision because..... There is more lateral inhibition at the intersection than in the middle of a white bar. Receptive fields are smaller in the fovea (center of vision) than away from the fovea. Lateral Inhibition & Edge Detectors

Psych 355, Miyamoto, Spr '15 19 Edge Detectors and Bar Detectors in Visual Cortex Lateral inhibition helps neurons to work together to create edge and bar detectors. Lateral inhibition enhances the perception of edges. Anderson, Figure 2.07 Anderson, Figure 2.09 More Evidence for Feature Detectors – Motion Aftereffects

Evidence for Motion Detectors – Motion Aftereffects Waterfall Illusion (this is one of the original discoveries that lead to the study of motion aftereffects) Click on the "Waterfall Illusion" Expanding Buddha: ♦ Set the display to "Full Screen". Choose whether you want the Buddha to expand or contract. Then click "start." Motion aftereffects give evidence for motion detectors in the visual system. ♦ Persistent activation of a motion detector reduces its sensitivity (adaptation). When the motion is stopped, we “see” motion in the opposite direction. ♦ These motion aftereffects support the general claim that there are feature detectors in the visual system. Psych 355, Miyamoto, Spr '15 20 Summary: Visual Feature Detectors

Psych 355, Miyamoto, Spr '15 21 Summary - Visual Feature Detectors Hubel & Wiesel used single-cell recordings to demonstrate the existence of feature detectors in the visual system. Lots of evidence for feature detectors: ♦ Single-cell recordings ♦ Visual illusions that can be explained by lateral inhibition (inhibition of neighboring neurons) ♦ fMRI evidence (not discussed in this lecture) Many different types of neural feature detectors have been found: edge and bar detectors, motion detectors, texture detectors, color detectors, etc. Important Hypothesis: Many perceptual and cognitive processes are based on feature representations. END