1.1 Phenomena in Transcription Typing

After Salthouse’s [1986a] review of the 29 behavioral phenomena in transcrip-tion typing, additional phenomena have been identified and summarized. John [1988] summarized 2 behavioral phenomena discovered by other researchers [Gentner 1983; John 1988; Salthouse and Saults 1987]. In addition, three eye-movement phenomena and one neural imaging pattern in transcription typing have been discovered [Inhoff et al. 1992c; Rayner 1998]. These 34 phenomena are introduced in Table I as six categories [Salthouse 1986a] including basic phenomena, units of typing, typing error, skill effects, and eye-movement phe-nomena.

1.1.1 Basic Phenomena. The following 12 behavioral phenomena are cate-gorized as the basic phenomena in transcription typing by Salthouse [1986a] and they are related to the major factors affecting the interkey time, compar-ison of transcription typing with other tasks, and concurrent tasks in typing. Interkey time refers to the interval between two adjacent keystrokes, and is regarded as the basic measurement of human performance in transcription typing.

—Phenomenon 1. Typing is faster than choice reaction time. Salthouse [1984a] reported that the median interkey time for skilled typists was 177ms, while the typical reaction time for a two-choice reaction time task is about 300-400ms. Based on Hick’s law on choice reaction time, a typical binary choice reaction time is 150+170Чlog2(2)=320ms [Schmidt 1988].

—Phenomenon 2. Typing is slower than reading. Salthouse [1984a] found that the reading speed of the typists in his experiments was 253 words-per-minute (wpm), but their typing speed was only 58 words-per-minute.

—Phenomenon 3. Typing skill and comprehension are independent. In-volvement of comprehension is optional while typing [Salthouse 1986a]. Nonsignificant correlations were reported between net typing speed and comprehension scores obtained in typing [Salthouse 1984a].

—Phenomenon 4. The rate of typing is nearly the same for random words as it is for meaningful text.

—Phenomenon 5. The rate of typing is slowed as the material approaches random. The difference between phenomena 4 and 5 is that the former refers the order of the words being randomized, while the latter refers to the order of characters within each word being randomized. It was found that the average interkey time in typing increased to 454ms when subjects are typing materials composed of words with random characters [Hershman and Hillix 1965].

—Phenomenon 6. The rate of typing is severely impaired by a restricted pre-view of the material to be typed. Decreasing the number of characters to be typed in the restricted preview increased the interkey time and severely impaired the typing rate.

—Phenomenon 7. Alternate-hand keystrokes are faster than the same-hand keystrokes (called the alternate-hand advantage). Successive keystrokes from fingers on alternate hands are 30-60ms faster than successive key-strokes from fingers on the same hand.

—Phenomenon 8. Digram (letter pairs) that occur more frequently in nor-mal language are typed faster than less frequent digram (called the digram frequency effect). The significant difference in typing speed between the low-frequency digrams and the high-frequency digrams has been reported in numerous studies [Salthouse 1984a; 1984b].

—Phenomenon 9. Interkey time is independent of word length. Salthouse [1986a] summarized several experiments in transcription typing and found no significant difference between the interkey time in typing long words and short words.

—Phenomenon 10. The first keystroke in a word is slower than the subsequent keystrokes (called the word initiation effect). Salthouse [1986a] reviewed 5 researchers’ experiments and found that the interval before the first key-stroke in a word is approximately 20% (45ms) [Salthouse 1984a] longer than that between the later keystrokes in the word.

—Phenomenon 11. The time for a keystroke is dependent on the specific con-text in which the character appears, especially for the topography of the keyboard (called the context phenomenon). The specific context here refers to the character ahead of and behind the target character. The context phe-nomenon is a combination of the alternate-hand advantage (phenomenon 7), the digram-frequency effect (phenomenon 8), the word-initiation effect (phe-nomenon 10), and, more specifically, the effect of topography of the keyboard in interacting with prior and subsequent keystrokes. For example, in typ-ing the key sequence “r-e”, the close proximity of the two keys “r” and “e” in the same row on a standard QWERTY keyboard allows the middle fin-ger on the left hand to move toward the target “e” while the index finger on the left hand is typing character “r”, which may save half of the movement distance of the middle finger from the home position “d” to the target position “e”.

—Phenomenon 12. A concurrent task does not affect typing performance. For highly skilled typists, a concurrent activity can be performed with little or no effect on the speed or accuracy of typing. Salthouse and Saults [1987] added a secondary task in parallel with the primary task of transcription typing: typists were asked to press a foot pedal as soon as they heard a tone signal [Salthouse and Saults 1987]. They found that the interkey time in this concurrent task situation was 185ms, which was not significantly longer than that in a single task situation (transcription typing only, interkey time 181ms).

1.1.2 Units of Typing. This group contains six phenomena related to the various spans and units of typing (defined later), five of which appeared on the original list of Salthouse [1986a] and the last one was identified after the list was published [Salthouse and Saults 1987]. It was regarded as one of the post 29 phenomena (phenomenon 30) by John [1996].

—Phenomenon 13. Copying span is 2-8 words or 7-40 characters for all typ-ists. Copying span is the amount of characters that can be typed accurately after a single inspection of the copy [Salthouse 1986a]. Without requiring the typists to commit the material to be typed to memory before typing or by randomizing the order of the words, Salthouse [1985] measured the copying span as the number of characters typed correctly after an unexpected disap-pearance of the copy and found that the copying span in normal transcription typing situation was 14.6 characters on average for the skilled typist.

—Phenomenon 14. Stopping span is one or two characters. Stopping span is the number of keystrokes typed after the subjects were requested to ter-minate their typing immediately after perceiving a stop signal. Using an auditory stop typing signal, Logan [1982] found that the stopping span was 2.16 characters when the typing materials were sentences.

—Phenomenon 15. Eye-hand span is 3-8 characters. Eye-hand span is defined as the number of characters intervening between the character whose key is currently being pressed and the character receiving the attention of the eyes [Salthouse 1986a]. Butsch [1932] found that the eye-hand span was 5 characters. The result is consistent with the other studies reviewed by Salthouse [1986a] who found that the range of eye-hand span is between 3 to 8 characters.

—Phenomenon 16. Eye-hand span is smaller for unfamiliar or meaningless material than for normal texts. When typists were typing a text and each word in it was composed of randomly ordered letters, Salthouse [1984a] found that their eye-hand span was only 1.75 characters.

—Phenomenon 17. Replacement span is about 3 characters. The subjects in Salthouse and Saults [1987] were asked to type exactly what appeared on the screen where one of the characters to be typed could be suddenly re-placed by another character. Replacement span is defined as the keystroke-replacement interval corresponding to a 0.5 probability of typing the second (replaced, i.e., newly appeared) character. The replacement span was 2.9 characters on average [Salthouse 1986a].

—Phenomenon 30. Detection span is about 8 characters. In the experiment of Salthouse and Saults [1987], subjects were asked to press the “/” key when they noticed a capital character on the line. The detection span is defined as the number of characters intervening between the capital character and the character currently being typed. The observed mean detection span was 8 characters approximately.

1.1.3 Errors in Transcription Typing. Salthouse [1986a] classified the vast majority of typing errors into four categories: substitution (e.g., work for word), intrusion (e.g., worrd for word), omission (e.g., wrd for word) and transposition (e.g., wrod for word). He summarized five major typing error phenomena re-lated to these four categories of errors.

—Phenomenon 18. 40%-70% of typing errors are detected without reference to the typed text. After reviewing three studies in transcription typing, Salt-house [1986a] summarized that about 40%-70% of typing errors are detected without reference to the typed copy. In his review, Salthouse suggested that typing errors include: (a) undetected errors which can be postulated to orig-inate at earlier levels of processing (errors mainly caused by failure to pre-serve sequences in the sensory and working memory) and (b) detected errors without reference to the typed copy which probably stem from later stages of processing (hand and finger movement) that are handled by the efferent response feedback.

—Phenomenon 19. Many substitution errors involve adjacent keys. Exper-imental results from highly skilled typists indicated that 30.1% of substi-tution errors involved horizontally or vertically adjacent keys [Salthouse 1986a].

—Phenomenon 20. Many intrusion errors involve extremely short interkey time in the immediate vicinity of the error. Nearly 38% of the intrusion error keystrokes had ratios (interkey time of an error keystroke divided by that of the regular interkey time) less than 0.1 of the average interkey time [Salthouse 1986a] and over 54% of intrusion errors involved an adjacent key in the same row or the same column.

—Phenomenon 21. Many omission errors are followed by a keystroke interval approximately twice the overall median. Salthouse [1986a] summarized this phenomenon based on Shaffer’s study [1975] which found that the interkey time of the keystroke right after the omission error was 1.54 times longer than that of the average interkey time.

—Phenomenon 22. Transposition errors mostly occur cross-hand. Salthouse [1986a] reported that 80% of the transposition errors were typed by the op-posite hands.

1.1.4 Skill Effects in Transcription Typing. Salthouse [1986a] summarized seven phenomena related to the improvement of typing performance through practice. In addition, Gentner [1983] found another related phenomenon—the interkey time of transcription typing decreases with practice following the power law, which is listed in the following as one of the post 29 phenomena (phenomenon 31).

—Phenomenon 23. Digrams typed with two hands (two-hand digrams) or with two different fingers of the same hand (two-finger digrams) exhibit greater changes with the skill level of typists than do digrams typed with one finger. Salthouse [1984a] found that the slope of the regression equations relating the digram interval to typing speed of two-hand digrams (-2.08) and two-finger digrams (-2.38) were greater than that of one-finger digrams (-1.38 on average).

—Phenomenon 24. Repetitive tapping rate increases with the skill level of typists. Salthouse [1984a] found a significant positive correlation between the tapping rate and the net typing speed ( p <.01).

—Phenomenon 25. The variability of interkey time decreases with the skill level of typists. Salthouse [1984a] found that two types of variability of the interkey time (75% quartile-25% quartile) decreased with an increase in typists’ skill level: (a) Inter-keystroke variability, which refers to the distri-bution of interkey time across different keystrokes and different contexts, correlated -.69 with the net typing speed; (b) Intra-keystroke variability, which represents the distribution of interkey time for the same keystroke in the same context but across multiple repetitions, correlated -.71 with the net typing speed.

—Phenomenon 26. Eye-hand span is larger with increased skill level of typists. In the Salthouse [1984b] studies, the correlation between the eye-hand span and net words-per-minute across 74 typists was significant with p <.01. There was an increase of between 0.5 and 1.2 characters with every 20 net words-per-minute increase in typing skill [Salthouse 1985; Salthouse and Saults 1987].

—Phenomenon 27. Replacement span is larger among more skilled typists. Salthouse’s studies [1985] found that the correlation between net words per minute and the replacement span was 0.80 ( p <.01).

—Phenomenon 28. Copying span is moderately related to the skill level of typists. The correlation coefficient between copying span and net words-per-minute ranges from 0.35 to 0.57 [however, the correlation is not significant, p >.05 Salthouse [1985].

—Phenomenon 29. Fast typists have larger stopping spans than slow typists. The experimental results of phenomenon 29 are not conclusive. Salthouse and Saults [1987] reported a correlation of 0.57 between the typing speed and the stopping span. However, another study of Salthouse [1985] did not find any significant correlation between these two variables ( p >.05).

—Phenomenon 31. Interkey time of transcription typing decreases with prac-tice following the power law of practice [Gentner 1983]. Typing speed of an unskilled typist can be improved to that of a skilled typist. According to the learning curve of the single typist in the study of Gentner, the improvement of interkey time follows the power law of practice.

1.1.5 Eye-Movement Phenomena. Although not included in the Salthouse list of phenomena, eye movements are one of the most important aspects of hu-man behavior in eye-hand coordination tasks including transcription typing. Among the various variables in eye movements data, fixation duration (the length of time for one fixation of the eye movements), saccade size (the number of characters or the degrees of visual angle between two fixation points) and gaze duration-per-character (equals fixation duration divided by saccade size) are the major parameters in determining eye movements in transcription typ-ing [Inhoff et al. 1992a; 1992b]. Three recently discovered eye movements phenomena related to transcription typing are listed here.

—Phenomenon 32. Gaze duration-per-character decreases with increased pre-view window size. Inhoff et al. [1992a; 1992b] found that the gaze duration-per-character decreased from 280ms to 182ms when the preview window size increased from 1 to 11 characters.

—Phenomenon 33. The mean saccade size is about 4 characters [Rayner 1998].

—Phenomenon 34. The mean fixation duration in transcription typing is 400ms [Rayner 1998].