Description Usage Format Details Note Source References See Also

Rothkopf's (1957) Morse code data of discrimination
probabilities among *36* auditory Morse code signals for the
letters *A*, *B*, ..., *Z* and the digits *0*,
*1*, ..., *9*.

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The `morse`

data frame consists of *36* rows and *36*
columns, representing the Morse code signals for the letters and
digits *A*, ..., *Z*, *0*, ..., *9* presented
first and second, respectively. Each number, an integer, in the
data frame gives the percentage of subjects who responded
‘same’ to the row signal followed by the column signal.

Each signal consists of a sequence of dots and dashes. A chart of the Morse code letters and digits can be found at http://en.wikipedia.org/wiki/Morse_code.

Rothkopf's (1957) *36x36* Morse code data
gives the same-different judgements of *598* subjects in
response to the *36x36* auditorily presented pairs
of Morse codes. Subjects who were not familiar with Morse code
listened to a pair of signals constructed mechanically and separated
by a pause of approximately *1.4* seconds. Each subject was
required to state whether the two signals presented were the same or
different. Each number in the `morse`

data frame is the
percentage of roughly *150* subjects.

The original Rothkopf's (1957) *36x36*
dataset does not satisfy regular maximality. There are two maximal
entries in row \#*2*, of value *84*, which are
*p\_BB* and *p\_BX*. Following the
argument in Dzhafarov and Colonius (2006), a statistically
compatible dataset is obtained by replacing the value of
*p\_BX* with *83* and leaving the rest of the data
unchanged. The latter is the dataset accompanying the package
`fechner`

.

For typographic reasons, it may be useful to consider only a small
subset of the stimulus set, best, chosen to form a
‘self-contained’ subspace: a geodesic loop for any two of the
subset's elements (computed using the complete dataset) is contained
within the subset. For instance, a particular self-contained
*10*-code subspace of the *36* Morse codes consists of the
codes for the letter *B* and the digits *0*, *1*,
*2*, *4*, ..., *9* (see `fechner`

).

Rothkopf, E. Z. (1957) A measure of stimulus similarity and errors
in some paired-associate learning tasks. *Journal of
Experimental Psychology*, **53**, 94–101.

Dzhafarov, E. N. and Colonius, H. (2006) Reconstructing distances
among objects from their discriminability. *Psychometrika*,
**71**, 365–386.

Dzhafarov, E. N. and Colonius, H. (2007) Dissimilarity cumulation
theory and subjective metrics. *Journal of Mathematical
Psychology*, **51**, 290–304.

Uenlue, A. and Kiefer, T. and Dzhafarov, E. N.
(2009) Fechnerian scaling in **R**: The package fechner.
*Journal of Statistical Software*, **31**(6), 1–24.
URL http://www.jstatsoft.org/v31/i06/.

`check.data`

for checking data format;
`check.regular`

for checking regular
minimality/maximality; `fechner`

, the main function for
Fechnerian scaling. See also `wish`

for Wish's
Morse-code-like data, and `fechner-package`

for general
information about this package.

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