Input/Output Modalities
CSD 823X Spring 2011
John B. Eulenberg, Professor
Three Input Modes
• Direct Selection
• Encoding
• Scanning
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Serial Scanning
Directed Scanning
Single-Switch vs. Double-Switch
Row-and-Column Scanning
Definition: Language Space
• The spatial arrangement of the terminal symbols of the universe of
linguistic elements at any one level of linguistic abstraction
• Examples:
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–
–
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Vowel space in the oral cavity
Letters on a keyboard
Word-squares on a language board
The 7 keys on the BAT chordic keyboard
“Terminal Symbols”
• The ultimate symbols that one uses to
construct an utterance.
• Examples:
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–
–
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Phonemes
Letters
Pictures or Pictograms
Switch-Chords on a chordic keyboard
Direct Selection
• Direct Selection pertains to a language space where
all the ultimate units are accessible. This is usually
a rather large set of symbols
• Examples:
– Computer Keyboard accessed by hand-finger movement (typical
“normal” access)
– Squares on a touch screen (e.g. DynaVox) accessed by head stick
– Joystick with separate individual rest places (detented joystick)
– Language board accessed by hand/finger pointing
– Eye gaze at a large number of symbols
Encoding
• Encoding is used when the communicating person can hit a
few items (not just one, but not a lot) at a time.
• Examples:
– Morse Code (where one chooses one of TWO items)
– Eugene Chernyakhovsky’s language board, where the periphery
presented the numbers from 0 to 9, and each item was encoded
with an index number from 0 to 999 (see “Eugene”)
– Julie Hastings’s hand control, with which shiactivated one of six
switches, in pairs, so she could point to one of 36 items.
Julie Hastings System
1
2
3
4
5
1
2
3
4
5
Julie’s fingers map in pairs of numbered
switches to one of 36 cells.
6
1-1=A, 1-2=B,…3-4=L...
6
Scanning
• Used primarily when the number of items
that can be accessed at any time is just two
(on/off, hit switch or not hit switch, blink or
not blink)
• A binary choice is made as items are
presented by another person or by a device
Serial Scanning
• In serial scanning, items are presented one
after another, from first to last.
• Example:
– Presenting the alphabet as ‘A, B, C,….X,
Y,Z’ to a person, waiting for the person to
squeeze your hand when you get to the letter
she/he wishes to add.
Average Cost for Getting A
Letter (in time units)
Serial Scanning -- 26 Letters
Average Letter will take 13 time units
Minimum is 1
Maximum is 26
Most Frequent Letters in English
Text:
ETAOIN SHLDRU
Row-and-Column Scanning
• Items are arranged in rows
• User first selects a row, as rows are
presented in sequence
• User then selects the item in a row (column
select)
Cost of Getting a letter in a Row
and Column Arrangement
Five Rows, So
average cost of
row is 2.5 units.
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
Maximum cost
(YZ) is 10
P
Q
R
S
T
Average Cost to
get to a letter 5
U
V
W
X
Y/Z
Five Columns, so
average cost to
get to item is 2.5.
Minimum Cost
(A) is 2
Directed Scanning
• This is half-way between a direct-access
joystick and row-and-column scanning.
• The user is more “in control” than in rowand-column scanning, but it is slower than a
direct-access joystick.
• In Directed Scanning, you use a joystick to
indicate the direction of the scan, while the
items are scanned one-by-one.
Single-Switch vs. Double-Switch
• Single-Switch Scanning: The switch is used
both for choosing rows and columns
• Double-Switch Scanning:
– Switch 1 is used for advancing the cursor
– Switch 2 is used for activating the current choice
(whether row or item in row)