Visual Perception CS4390/5390 Fall 2014 Shirley Moore, Instructor September 8,

Announcements Dr. Moore’s office hour today is at 2pm instead of 3pm CS Seminar, Dorian Arnold, UNM, 3-4pm Thursday Sept 11, “Scalable Middleware and Tools for High Performance Computing”, location TBD HW1 grades posted on BlackBoard Reminder: NSF/Popular Science Vizzies deadline Sept 30 2

From last class: Class Exercise 2: Location Data for the Map Now let’s draw a red circle in the center of each state, with the size of the circle representing the state’s population. Download the following two files and add them to the sketch: – – – The second file contains code to read the data in the first file into a table. Find population data on the Web and add the data to the sketch. Draw the required circles on the map. Add rollovers to show the state name and population when the mouse hovers over it. 3

The Human Eye 4Image credit:

Retina with Rod and Cone Cells Image credit: 5

Distribution of “brain pixels” (Ware 2008) 6

Visual Cortex Image credit: 7

Visual Attention We apprehend only a tiny amount of the visual information in our surroundings. We sample the visual world on a need-to- know basis. Visual attention consists of a series of visual queries – eye movements – pattern matching Both bottom-up and top-down processing 8

Stages of Visual Cognition Feature processing – Parallel processing of visual field by billions of neurons in V1 area of visual cortex – Orientation and size, red-green, yellow-blue, direction of motion Pattern construction – Visual space divided into regions – Chains of features connected to form contours Object formation – Features and patterns distilled into visual objects – About three visual objects can be held in visual working memroy at one time. – Objects linked to non-visual information 9

Implications for Visual Design Analyze visual tasks Break tasks down into visual queries Design displays so that visual queries can be processed correctly and quickly for every important cognitive task – Support the most important and frequent visual queries with visually distinct symbols Example: public transit map 10

Visual Distinctness Based on early low-level feature processing system If we are looking for something small, we can only see it when we are lookng at it. How do our eyes get directed to the right location – Visual scanning – Biased shouting mechanism Want target to be distinct in some feature channel of the V1 area Hard-wired in the brain, not learned 11

Basic Feature Channels 12

Do any circles appear distinct? 13

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Find the symbol that is different 18

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Conjunction 20

Visual Conjunction Trying to find a target based on two features Most visual conjunctions hard to see Neurons sensitive to conjunctive patterns are farther up the processing pathway and cannot be used to plan eye movements. 21

Motion Motion generates an orienting response. Most powerful orienting response is elicited by things that move into the visual field. Hard to suppress orienting response – use sparingly! 22

Visual Search Process – Where’s Waldo? Image credit: eye-tracking-only-registers-half-of-the-visual-search-process/ 23

Preparation for Next Class Read Ware Chapter 4 and Munzner Chapter 10 on Color Continue working on Lab 1 – Bring questions and problems to class on Wednesday! 24