Chapter 5

Visual Attention and Information that Pops Out

Searching the visual field

• The attention process is focused around the fovea where vision is most detailed:

• Useful field of view: varies greatly depending on the task and the displayed information

• 1-4 degrees normal, up to 15 degrees in certain situations

• Size varies with target density

Reading from the iconic buffer

• Visual buffer is called ICONIC MEMORY

• If an image is shown for 1/10 sec, the iconic memory can store it for 2/10 sec.

Reading from the iconic bufferPreattentive processing

• Some shapes or colours POP OUT - they are preattentively processed

• Prior to conscious attention

• The time to find it is the same no matter the amount of distractors

• Processed faster than 10 ms

• Useful to quickly convey information ”at a glance”

Reading from the iconic bufferPreattentive processing

• Some shapes or colours POP OUT - they are preattentively processed

• Two important factors:

• degree of difference of target from non-targets

• degree of difference of non-targets from each other

• Sometimes important that each of many symbols are preattentively distinct from all other, for example in maps

• Better to add marks to highlight instead of removing them

Reading from the iconic buffer Preattentive processing

Reading from the iconic bufferConjunction search

• A serial search of complex patterns

• Generally not preattentive

• Exceptions:

• spatial grouping

• stereoscopig depth

• convexity, concavity, colour

• motion

Reading from the iconic bufferHighlighting

• A way to make information stand out

• Rule of thumb: use whatever graphical dimension least used otherwise in the design

• Blurring irrelevant details: highlighting using semantic depth of field

Neural processing...Neurological evidence for preattentive

processing

• The visual system can perform massively parallel processing for incoming signals:

• Several billion neurons in V1 & V2 to analyse signals from only 2 million nerve fibers.

• Accounts for > 40% visual processing

Neural processing...Neurological evidence for preattentive

processing

• Tuned receptive fields: devices that responds strongly to specific patterns

• In V1 and V2 there are cells tuned to different properties

• Orientation and size with lumincence (Gabor)

• Colour

• Elements of local stereoscopic depth

• Elements of motion

Neural processing...Graphemes

• The smallest elements from which perceptual objects are constructed

• A graphical element which is primitive in visual terms

• To create efficient visual patterns we must understand what patterns the tuned cells respond to best

Neural processing...The Gabor Model

• The Gabor function is THE IDEAL GRAPHEME for generating visual texture

• Mathematical function describing the receptive field properties

Texture coding information

• Texture elements should have a dominant orientation and spatial frequency

• Three parameters: orientation, scale and contrast

Texture coding informationPercentually independent information

• If displaying many different kinds of information:

• display methods must be PERCEPTUALLY INDEPENDENT

• Information carried on one channel must not interfere with information on another

Texture coding informationPercentually independent information

• Perceptually independent texture

• Orientation: > 30 degree difference is easily distinguished

• Resolution: resolvable size difference > 9% size change

Texture coding informationTexture contrast effects

• Texture size can appear distorted because of contrast effects just like luminance contrast illusions (Ch.3)

Texture coding informationTexture contrast effects

• This will cause errors in reading data that is mapped to texture element size

• Texture orientation can cause contrast illusions in orientation as well

Glyphs and Multivariate Discrete Data

• A glyph is a visual object mapping information

• When designing glyphs we need to consider what is preattentively processed

Glyphs and Multivariate Discrete DataIntegral or separable display dimension

• With integral display dimensions attributes are perceived holistically and not independently

• For separable display dimensions attributes are perceived independently.

Glyphs and Multivariate Discrete DataSpeeded classification tasks

• Tells us how glyphs visually interfere with each other

• Subjects classify visual patterns according to only one attribute

• The other attribute can be random (interference) or connected to the first attribute (redundant)

• Integral dimensions: redundant coding helps, random coding interferes

• Separable dimensions: redundant and random coding is fairly neutral

Glyphs and Multivariate Discrete DataIntegral separable dimension pairs

• If subjects should respond to the glyph only: use integral

• If subjects should think about the values of the glyph: use separable

• Overly simplistic

• There is always some interference even between the most separable dimensions

• Simplistic makes it a good design guideline

Glyphs and Multivariate Discrete DataIntegral separable dimension pairs

• Simplistic makes it a good design guideline

Glyphs and Multivariate Discrete DataMonotonicity

• A visual quality can be monotonic

• Increases / decreases continuously

• bigger than, brighter than...

• E.g. orientation is NOT monotonic

• Good attributes for representing quantity: size, lightness, darkness, vividness, height above ground

Glyphs and Multivariate Discrete DataMultidimensional Discrete Data

• Graphical attributes that may be used in glyph design

Exam questions Chapter 5

How large is the (standard) Useful Field of View?A, 4-7 degreesB, 1-4 degreesC, 3-6 degreesD, 6-9 degreesE, 2-5 degrees

Which of the following is NOT preattentively processed?A, OrientationB, ConvexityC, SizeD, ParallelismE, Motion

Which of the following is not preattentively processed:A. MotionB. OrientationC. Convexity / ConcavityD. ParallellismE. Basic shape

How many objects can we count "at a glace", without having to explicitly start counting?A. 1B. 2C. 4D. 6E. 7

Which of the following information is not true?A. The cells in V1 and V2 are differentially tuned different orientation and size, elements of local stereoscopic depth, spatial position and elements of motion.B. "The pattern that most efficiently excites a neuron in the visual system is exactly the pattern that the neuron is tuned to detect"-is the basis of the Grapheme Concept.C. The most efficient grapheme is one that matches the receptive field properties of some class of neurons.D. To create efficient visual patterns, its very important to understand the kind of patterns the tuned cells of the visual cortex respond to the best.E. Gabor function is a widely used mathematical model to describe the receptive field properties of the neurons reside in V1 and V2.