Movement kinematics of the braille-reading finger

Abstract: A new means of measuring the movement properties of the braille- reading finger is described and exemplified in an experiment in which experienced readers of braille encountered sentences comprised of keywords in which word and orthographic frequencies were manipulated. These new data are considered in theoretical and practical terms. ********** Individuals who read braille (hereafter, braille readers) face a three-pronged challenge: to decode braille as patterns of texture at the moving fingerpad or fingerpads, to extract the linguistic meaning of the braille code, and to coordinate the movements of reading fingers with perceptual and linguistic processing. These are distinct operations whose features, individually and in combination, are important to describe if braille reading is to be better modeled as a complex perceptual-cognitive-motor skill. To the naked eye, braille readers' performance reveals important properties: reading is predominantly serial, rather than parallel (the braille cells are encountered one at a time); it is continuous, rather than stop-start; and, since words are not jumped over or skipped, it is exhaustive, rather than selective. Developments in recording methods offer a higher-resolution view of how braille reading occurs in time and space, which can lead to more empirically quantifiable descriptions of reading performance. Bertelson and his colleagues (Bertelson, 1995; Bertelson, Mousty, & D'Alimonte, 1985; see also Noblet, Ridelaire, & Sylin, 1985) developed a method of computer-controlled sampling (every 40 milliseconds) of the position of a light-emitting diode attached to a reading finger or fingers. Such recordings revealed important new data, including the extent to which two-handed braille readers move the fingers together on a line of text in the same direction at the same velocity ("conjoint" movements) and the extent to which they produce "disjoint" movements. Millar (1997) developed a means of analyzing reading data by using video recordings that were subjected to frame-by-frame marking (at 40 milliseconds per frame). This method gave rise to important data on reading rates, to accounts of how these rates vary among readers with different levels of proficiency and different text content, and to descriptions of the varieties of reading-finger reversals of direction. Breidegard and colleagues (2008) developed a computer-based means of analyzing video frames from 25-hertz cameras for the recovery of data on position and the representation of paths of reading scans. These techniques reveal crucial details of the braille-reading finger that are not reliably clear to either the naked eye of an observer or to conscious introspection by the reader. They also expose another layer of questions. For example, the recordings reveal that two-handed readers are frequently in contact with and move across two distinct portions of the text at the same time. Whether this means that a reader can be said to be reading two passages at the same time, is processing each passage in some alternating manner, or is using some other strategy is not clear (compare Bertelson & Mousty, 1989; Millar, 1987). Hughes, Van Gemmert, and Stelmach (2011, in press) used digitized data on finger positions (sampled at 100 hertz or every l0 milliseconds), rather than video recordings, to derive data on velocity and acceleration during braille reading. The sampling frequency was high enough to permit computations of velocity and acceleration. Emerging from such recordings were new data on how reading is executed. Foremost was evidence that in all conditions the single dominant reading finger moves within a broad velocity range (1-10 centimeters, or 0.4-4 inches, per second), with averages approximating 3 centimeters (or 1.2 inches) per second, but without ever being smooth or constant. Hughes and colleagues found that instantaneous finger velocity tends to fluctuate continuously between phases of acceleration and deceleration (producing so-called zero-crossings in the acceleration trace). …