Short-term memory for position and hemisphere advantage
in hearing and deaf signers and nonsigners
Allegra Cattani & J. Clibbens
University of Plymouth, UK
To investigate the visual short-term memory consequences of altered sensory and language
input early in development, we studied visual memory for position in deaf signers and nonsigners who had been auditorily deprived since birth and hearing signers and non-signers.
The present work is the first attempt within the visuo-spatial cognition field to investigate a
comparison study of a large sample (N=97) of four groups of participants involving deaf
signers (N=28) and non-signers (N=18) versus hearing signers (N=20) and non-signers
(N=31). In this way, we could compare the effects of deafness per se regardless of the effect
of acoustic feedback and separately the effect of the presence/absence of acoustic feedback
regardless of the effect of the signed and vocal language used.
Although a decade ago only a handful of studies had attempted to systematically study the
non-linguistic aspects of spatial cognition in deaf signers, recent studies involving mental
imagery and motion perception and detection have investigated the brain reorganization
documenting effects of sensory deprivation or sign language use. Results from studies with
deaf signers (Neville & Bavelier, 2002; Bavelier, Brozinsky, Tomann, Mitchell, Neville &
Liu, 2001; Bavelier, Tomann, Hutton, Mitchell, Corina, Liu, & Neville, 2000; Finney &
Dobkins, 2001; Bosworth & Dobkins 1999; Neville & Lawson, 1987) suggested that visual
perception in the deaf may be altered as a result of their auditory deprivation – this is the so
called auditory deprivation hypothesis. Alternatively, altered visuo-spatial cognition in the
deaf may arise as a result of their acquisition and use of sign language (Emmorey, Kosslyn
and Bellugi, 1993, Emmorey and Bettger, 1995; Chamberlain and Mayberry, 1994) – this is
the so called sign language hypothesis.
In Study 1 we used a similar methodology to that of Neville & Bellugi (1978). The task was
to determine whether a circle seen consecutively twice on a computer screen was placed in
the same or a different position. Participants responded by pressing a key. In this way, no
digit or letter was included in order to avoid any confounding effects with numerical or
alphabetical processes. Furthermore, to analyze the lateralization effect we introduced a
variant task where the circle was presented inside a grid of rectangles. In this way, the
categorical (e.g., an equivalence class such as above, below, left of, right of) and coordinate
(e.g., metric spatial properties) spatial relation representations (Kosslyn, 1987; Emmorey and
Kosslyn, 1996) were also investigated. We believed that the grid condition may help
participants as a “cue” (coded by vocal or signed language) to recall the location of the circle.
Within the grid background condition the stimuli are categorized and identified by the
participant in terms of the categorical spatial relation representation (for example in the task
“identify the position of a circle in a grid” the participant can use as a strategy ‘the circle is in
the upper left rectangle’ in - vocal or signed - language). Blank background stimuli are
identified within a coordinate spatial relation representation (for example in the task “identify
the position of a circle in a blank space” the participant does not use any vocal or sign
description which can help him but uses only spatial cues such as near-far-same). Results
showed that the use of sign language enhanced memory for position of a circle. The auditory
deprivation hypothesis explained the relative enhancement. The deaf (regardless of sign
language use) showed an atypical lateralisation compared to the hearing groups. The hearing
showed a normal hemisphere advantage in terms of Kosslyn’s (1987) proposal of categorical
spatial relation representations in the left hemisphere and coordinate spatial relation
representations in the right hemisphere. By contrast, the deaf showed an atypical hemispheric
advantage for categorical spatial relation representations in the right hemisphere and
coordinate spatial relation representations in the left hemisphere.
In Study 2, we investigated memory for position of a picture. The task was similar to Study
1, as participants had to make the same kind of decision but based on the position of a
drawing of an object or of an irregular shape. Our purpose was to investigate the effects of
stimuli which might be given a linguistic cue (e.g. the name of the object) and stimuli with
no linguistic cue on the relative hemispheric advantage in hearing participants, then to
compare these effects with the other three populations to see whether there were atypical
lateralisation effects. Furthermore, we wished to see whether there was any enhancement
effect in the deaf and signing populations. As in Study 1, the auditory deprivation hypothesis
explained the relative enhancement. The hearing participants (regardless of sign language
use) showed a right hemisphere preference for object location and no difference for the shape
location. The deaf showed a right hemispheric preference for the object location and a left
hemisphere preference for the shape location. Finally, results showed that both sign language
and auditory deprivation hypotheses explained the enhanced memory for position of a
picture.
In conclusion, our studies proved that both hypotheses had an effect on the overall
enhancement ability in visual short-term memory for location. Specifically, the atypical
hemisphere preference of the deaf was explained solely by the auditory deprivation
hypothesis.
References
Bavelier, D., Brozinsky, C., Tomann, A., Mitchell, T., Neville, H. & Liu, G. (2001). Impact
of early deafness and early exposure to sign language on the cerebral organisation for
motion processing. Journal of Neuroscience, 21, 8931-8942.
Bavelier, D., Tomann, A., Hutton, C., Mitchell, T., Corina, D., Liu, G., & Neville, H. (2000).
Visual attention to the periphery is enhanced in congenitally deaf individuals. Journal of
Neuroscience, 20, 1-6.
Bosworth, R. & Dobkins, K. (1999). Left hemisphere dominance for motion processing in
deaf signers. Psychological Sciences, 10, 256-262.
Emmorey, K. & Kosslyn, S. M. (1996). Enhanced image generation abilities in deaf signers:
A right hemisphere effect. Brain and Cognition, 32, 28-44.
Emmorey, K., Kosslyn, S.M. & Bellugi, U. (1993). Visual imagery and visual-spatial
language:enhanced imagery abilities in deaf and hearing ASL signers. Cognition, 46, 139181.
Finney, E.M. & Dobkins, K.R. (2001). Visual contrast sensitivity in deaf versus hearing
populations: Exploring the perceptual consequencies of auditory deprivation and
experience with a visual language. Cognitive Brain Research, 11, 171-183.
Kosslyn, S.M. (1987). Seeing and imaging in the cerebral hemispheres: a computational
approach. Psychological Review, 94(2), 148-175.
Neville, H. & Bavelier, D. (2002). Human brain plasticity: evidence from sensory
deprivation and altered language experience. Progress in Brain Research, 138, 177-188.
Neville, H.J. & Bellugi, U. (1978). Patterns of cerebral specialization in congenitally deaf
adults: A preliminary report. In P. Siple (Ed.) Understanding language through Sign
Language Research. New York: Academic Press, pp. 239-257.
Neville, H.J. & Lawson, D. (1987). Attention to central to peripheral visual space in a
movement detection task. III. Separate effects of auditory deprivation and acquisition of a
visual language. Brain Research, 405, 284-294.