Discusión

There is no general consensus regarding the set of basic handshapes in ASL (and also in other signed languages). Even though the different systems proposed for handshape

representation differ in the granularity of the features that serve as a basis for labeling handshapes, the notion of ‘selected fingers’ plays an important role in encapsulating the salient properties of a given handshape configuration. Selected fingers are a subset of

fingers that are salient in the articulation of a specific handshape [Liddell and Johnson,

1995,Brentari, 1998,Van der Kooij, 2002,Whitworth, 2011]. Examples of selected fingers within different handshapes and the different configurations of selected fingers in these handshapes are described further below.

Approaches for handshape representation can be broadly classified as follows:

• Representations that encode the joint positions for each of the different

(selected) fingers

These systems use the following parameters to represent each handshape configuration

– The subset of fingers that are selected (or, has salient properties in the articula-

tion of a specific handshape).

– The different degrees of bending/extension at the base and non-base joint angles

of the fingers. Liddell and Johnson [Liddell and Johnson, 1995] have suggested

four states {closed, hooked, extended, flattened } along with a symbol to denote a degree of flexibility in the muscle action (i.e., a relaxation in the encoded amplitude of folding/extension at a finger joint).

– The degree of spreading between different fingers (denoting abduction / adduc-

tion for the selected fingers).

– The different positions of the thumb with respect to the palm. Van der Kooij

[Van der Kooij, 2002] suggests the features {crossed, opposed, adducted, and, extended } along with an aperture feature (closed or open) that is useful when the thumb is in an opposed configuration to denote whether the thumb is in contact with the selected fingers.

An explicit representation for hand configuration allows for the precise encoding of a wide range of handshape configurations albeit at the expense of significantly ex-

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panding the state-space of representable handshape configurations. This substantially increases the model complexity for handshape inference and the annotation effort in- volved in labeling the ground-truth. The linguistic significance of many of these handshape configurations is also difficult to ascertain (“. . . these models may offer inventories of very detailed categories with numerous form elements often without

addressing their distinctiveness” [Demey and Van der Kooij, 2008]).

• Representations that are based on wholistic configurations of the hand

In approaches that enumerate wholistic configurations of the hand, an inventory of handshape forms is determined through an analysis of the different handshape con- figurations observed in sign language video datasets. Handshapes that are attested as producing articulatory contrast or those attested as conveying certain salient linguistic properties in signs are included in the inventory.

Many of the challenges that arise with employing an explicit encoding of hand con- figurations are circumvented to some extent in the handshape inventory approach. The latter approach sacrifices some precision in the transcription of specific hand- shape forms to provide a more compact representation. The smaller number of hand- shape distinctions facilitates handshape annotation in sign language video sequences as well as the development of computer models to represent the properties of hand- shape combinations in signs. We therefore adopt an inventory-based representation of handshapes in this research.

We utilize an inventory containing 85 handshapes to denote handshape configurations

in this work Figure2·3. Handshapes in this inventory were selected by linguists through an

analysis of approximately 10, 000 isolated (citation form) signs in the ASLLVD [Neidle et al.,

2012a] and 10, 500 utterances within continuous signing sequences from the ASLLRP [Nei- dle, 2013] video collection. Handshapes in the inventory are grouped based on similarity into different subsets. These groups of handshapes were created to aid the organization of handshape labels in the inventory and do not necessarily reflect linguistic affinity among

A 10 S cocked-S T X-over-thumb 1 D X bent-1 G/Q flat-G alt-G

U/H crvd-U bent-U cocked-U U-L bent-U-L V/2 crvd-V bent-V 3 crvd-3

6 W crvd-W 7 cocked-7 open-7 8 cocked-8 open-8 25 F/9 cocked-F open-F

4 5 crvd-5 5-C 5-C-L 5-C-tt

B B-xd flat-B B-L crvd-B crvd-flat-B crvd-sprd-B bent-B bent-B-xd bent-B-L

C sml-C/3 tight-C tight-C/2 O baby-O flat-O flat-O/2 fanned-flat-O E loose-E

M alt-M bent-M full-M N alt-N bent-N P/K alt-P L L-X crvd-L

R R-L I Y I-L-Y bent-I-L-Y Horns bent-Horns O/2-Horns

(a) Set of all handshape labels for ASL annotations in [Neidle, 2007].

B B-L flat-B 5 A S 1 D C Rlxd

(b) Unmarked handshapes in ASL.

Figure 2·3: The 85 handshapes in ASL labeled according to annotation conventions in [Neidle, 2007]: (a) The dominant signing hand can take any handshape from this set; (b) The handshape on the nondominant hand, when it differs from that of the dominant hand in a two-handed sign, is constrained to belong to the set of unmarked handshapes. Video sequences displaying multiple views of each of these handshapes in motion are available in [Neidle, 2011].

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different handshape configurations. The distinctions drawn in handshape configuration in- clude: different degrees of folding/extension of the selected fingers (e.g., {U, bent-U, curved- U, cocked-U}) and different positions of the thumb within the same basic handshape (e.g., {B, B-xd, flat-B, B-L}), different degrees of spread between the selected fingers (e.g., {crvd-B, crvd-sprd-B}) and different degrees of aperture of the hand (e.g., {O, flat-O, fanned-flat-O}).