Table 1.

Experimental studies on the role of vision in skilled handwriting reported in a chronological order.

Authors	Number of participants	Relevant comparisons	Experimental task	Data analysis	Main results and discussion
Smyth and Silvers (1987)	12 adults	V vs. VC vs. VB vs. NV vs. NVC vs. NVB	Writing of eight sentences	Writing time; Orientation of writing; Writing errors	The orientation of the written words was affected by the loss of vision rather than by the addition of a secondary task. The writing errors were very similar for the secondary task condition and the without-vision condition.
van Galen et al. (1989)	10 adults	V vs. NV	Writing a list of words, with similar vs. dissimiliar upstroke, with and without stroke repetitions within letters, and with long and short letters	MT of correct words	The deprivation of visual FB slowed down handwriting, especially in combination with the conditions that affect the short term memory.
Smyth (1989)	12 adults	V vs. NV	Writing nine letters, nine reverse letters, and drawing eight shapes	Number of strokes; Percentage of occasions on which two start and three progression rules were obeyed in visual and non-visual conditions; Writing errors	Without vision, movement production is simplified to reduce the number of relocations required. The use of consistent directions of movement depends of the ability to use visual control of spatial location.
Burton et al. (1990)	8 adults	V vs. NV in one-fourth, one-half, double, and four-times their normal size	Writing the words ‘poppy’ and ‘wood’	Width of each word; width of the space between the words; width of spaces between letters; width of individual letters; height of ‘tall’ letters (p, y, and d)	Size transformations were greater and closer to the instructed values with than without vision. Variability was greater with than without vision for all three space segments, with no significant effect of vision for any of the three letter segments. With vision, subjects differentiated letters and spaces in making their horizontal transformations; without vision, there was no differentiation.
van Doorn and Keuss (1992)	12 adults	V vs. NV, in the normal vs. short durations	Writing the sequence ‘lenehele’	RT; MT; Size; Spatial variability of the sequence; Variability of MT and Size	Spatial control was not affected by absence of vision but RT increased without vision, suggesting that invariance of shapes is preserved in the absence of vision at the expense of processing time increments.
van Doorn and Keuss (1993)	12 adults	V vs. NV	Writing the sequence ‘lelele’	Size; X/Y -ratio; Spatial variability	Geometric aspects of letters altered under no vision and under the scaling requirement to write in a small format.
Tamada (1995)	8 adults	Visual FB with various delays – 0, 33, 67, 100, 133, 167, 267, and 500 ms	Writing a word	Writing error rate	With increasing the delay, the writing error rate increased, especially in stroke repetition within words. (e.g., “feeling” as “feeeling”). Visual monitoring would be indispensable in producing stroke repetition.
Marquardt et al. (1996)	31 adults	Experiment 1: V vs. VT vs. NV vs. MT	Experiment 1: writing the sentence ‘Die Hunde bellen laut’	Number of Inversion in Velocity per stroke; Size	Vision is not required to produce automated handwriting movements and conscious attention to visual control hampers the elicitation of automated movements. Vision would be used to monitor script size even in highly automated handwriting.
		Experiment 2: VWT in normal size, 133 and 66% of the normal size	Experiment 2: writing ‘ll’ repeatedly for 8 s

V, writing with vision; VC, with vision while counting; VB, with vision while saying ‘blah’; NV, writing with no vision; NVC, with no vision and counting; NVB, no vision and ‘blah’; VT, visual tracking of the pen; MT, mental tracking; VWT, vision of the written trace only; MT, movement time; RT, reaction time.