Levels indeed! A response to Broadbent

David E. Rumelhart, James L. McClelland
1985 Journal of experimental psychology. General  
Although Broadbent concedes that we are probably correct in supposing that memory representations are distributed, he argues that psychological evidence is irrelevant to our argument because our point is relevant only at what Marr (1982) has called the implementation^ level of description and that psychological theory is only properly concerned with what Marr calls the computational level. We believe that Broadbent is wrong on both counts. First, our model is stated at a third level between the
more » ... d level between the other two, Marr's representational and algorithmic level. Second, we believe that psychology is properly concerned with all three of these levels and that the information processing approach to psychology has been primarily concerned with the same level that we are, namely, the algorithmic level. Thus, our model is a competitor of the logogen model and other models of human information processing. We discuss these and other aspects of the question of levels, concluding that distributed models may ultimately provide more compelling accounts of a number of aspects of cognitive processes than other, competing algorithmic accounts. Broadbent (1985) has generously conceded that memory is probably represented in a distributed fashion. However, he has argued that psychological evidence is irrelevant to our argument because the distributed assumption is only meaningful at the implementation (physiological) level and that the proper psychological level is the computational level. Broadbent has raised an extremely important issue, one that has not generally received explicit attention in the psychological literature, and we applaud his attempt to bring it into focus. However, the issue is very complex and deserves very close scrutiny. Indeed, more levels must be distinguished than Broadbent acknowledges, and there are many more constraints among levels than he supposes. We begin by pointing out that Broadbent has ignored a third level of theoretical description, the algorithmic level, which is a primary level at which psychological theories are stated. We then suggest that his analysis of our arguments fails to establish his claim that our model and traditional models are not competitors at the same level. We then describe other senses of levels, including one in which higher level accounts can be said to be convenient approximations to lower level accounts. This sense comes closest to capturing our view of the relation between our distributed model and Request for reprints should be sent to David E. Rumelhart, Institute for Cognitive Science C-015, University of California-San Diego, La Jolla, California 92093. traditional information processing models of memory. Marr's Notion of Levels Broadbent begins his argument by appealing to the analysis of levels proposed by David Marr (1982). Although we are not sure that we agree entirely with Marr's analysis, it is thoughtful and can serve as a starting point for seeng where Broadbent's analysis went astray. Whereas Broadbent acknowledges only two levels of theory, the computational and the implementational, Marr actually proposes three, the computational, the algorithmic, and the implementational levels. Table 1 shows Marr's three levels. We believe that our proposal is stated primarily at the algorithmic level and is primarily aimed at specifying the representation of information and the processes or procedures involved in storing and retrieving information. Furthermore, we agree with Marr's assertions that "each of these levels of description will have their place" and that they are "logically and causally related." Thus, no particular level of description is independent of the others. There is thus an implicit computational theory in our model as well as an appeal to certain implementational (physiological) considerations. We believe this to be appropriate. It is clear that different algorithms are more naturally implemented on different types of hardware, and therefore information about the implementation can inform our hypotheses at the algorithmic level. Broadbent's failure to consider the algorithmic 193
doi:10.1037/0096-3445.114.2.193 fatcat:s62uvvt6l5h6fo73newbps5dfe