the "dead and entombed manuscript" cannot do. As Leela Prasad states, "According to Shankara, the "correct tradition" (sampradaya) has as much authority as the written Shastra," explaining that the tradition "bears the authority to clarify and provide direction in the application of knowledge." The emphasis in this transmission is on the "proper articulation and pronunciation of the Vedic sounds", as prescribed in the Shiksha, the Vedanga (Vedic study) of sound as uttered in a Vedic recitation, mastering the texts "literally forward and backward in fully acoustic fashion." Houben and Rath note that the Vedic textual tradition cannot simply be characterized as oral, "since it also depends significantly on a memory culture." The Vedas were preserved with precision with the help of elaborate mnemonic techniques, such as memorizing the texts in eleven different modes of recitation (pathas), using the alphabet as a mnemotechnical device, "matching physical movements (such as nodding the head) with particular sounds and chanting in a group" and visualizing sounds by using mudras (hand signs). This provided an additional visual confirmation, and also an alternate means to check the reading integrity by the audience, in addition to the audible means. Houben and Rath note that a strong "memory culture" existed in ancient India when texts were transmitted orally, before the advent of writing in the early first millennium CE. According to Staal, criticising the Goody-Watt hypothesis "according to which literacy is more reliable than orality," this tradition of oral transmission "is closely related to Indian forms of science," and "by far the more remarkable" than the relatively recent tradition of written transmission. While according to Mookerji understanding the meaning (vedarthajnana or artha-bodha) of the words of the Vedas was part of the Vedic learning, Holdrege and other Indologists have noted that in the transmission of the Samhitas the emphasis is on the phonology of the sounds (śabda) and not on the meaning (artha) of the mantras. Already at the end of the Vedic period their original meaning had become obscure for "ordinary people," and niruktas, etymological compendia, were developed to preserve and clarify the original meaning of many Sanskrit words. According to Staal, as referenced by Holdrege, though the mantras may have a discursive meaning, when the mantras are recited in the Vedic rituals "they are disengaged from their original context and are employed in ways that have little or nothing to do with their meaning." The words