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In 2009, Joseph Lavanithum (University of Pretoria, South Africa) investigated whether pictures of signs help hearing mothers of young deaf children to remember the signs.
Four mothers participated in the study. The conclusion:
"It would appear that the sign illustrations were redundant during the initial stages of sign learning using a multimodal approach, but that they were relied on to trigger recall of signs during the self practice phase. Thus, the study confirmed the supportive role of sign illustrations in sign learning."
Click here, to read the entire report (in English)