The paper that was most responsible for reclaiming the visual side of working memoiy was Logie (1986). Logie's aim was to develop a form of visual suppression similar to the articulatory suppression used in the study of verbal working memory. Articulatory suppression is a very useful technique and has helped to uncover the organisation of verbal working memory. Logie aimed to develop a visual suppression task that, like articulatory suppression, has as minimal an attentional component as possible. He investigated the possibility of a visual part to the VSSP by presenting subjects with unattended pictures in the form of matrices, coloured squares or line- drawings. In initial experiments subjects made simple judgements about whether the currently presented pattern was identical to the pattern presented immediately before. In later experiments in the 1986 paper, however, Logie simplified this by removing the decision element of the task. Subjects were instructed to look at the screen but were told that the material was irrelevant to their task. Logie wanted to see whether this material had the same effect on visuospatial processing as unattended speech has on verbal material.
Instead of using the Brooks-type tasks that the earlier experiments in visual working memory had often relied on, Logie adopted the peg-words visual mnemonic task for the visual task and rote-rehearsal for a comparable verbal task. Logie reported that unattended visual material disrupted the use of a visual image-based mnemonic, while it had very little effect on rote rehearsal. Differing task difficulties made the findings of this paper less robust than they might have been. In addition, the details of the four experiments all differed from each other, presumably because Logie was still refining the techniques. Nevertheless the paper has been very influential.
It was an appealing idea that an unattended picture effect existed in visual working memory that corresponded to the unattended speech effect in verbal working memory. This seemed to give a neat symmetiy to the visual and verbal sub-systems. In addition, Logie's paper made it clear that there was more than just spatial coding in the VSSP. The fact that a task such as viewing irrelevant pictures, a task that does not emphasise spatial content, appeared to interfere with the pegword mnemonic drew researchers attention towards the probability that visual coding also had a part to play in the organisation of the VSSP, whether as part of a single system or, as Baddeley and Lieberman suggested, as a parallel store to the spatial sub-system. The paper was also very important in showing that the arguments for the VSSP being more spatial than visual were probably due to the nature of the secondaiy and main task used and that the coding in the store may be either visual or spatial.
While most researchers such as Quinn (1991) and Morris (1987) were focusing on the locus of disruption of spatial tasks, Logie and Marchetti (1991) investigated the locus of disruption within visual working memory. Quinn (1991) and Morris (1987) had
suggested that the mechanisms involved in encoding and retention may be different and had found little effect of visuospatial interference during maintenance of a spatial task. Interference was only found if the secondary visuospatial task was present during encoding. Like Quinn (1991), Logie and Marchetti argued that this may have come about because of the nature of the tasks that had been selected to reflect spatial processing. They suggested that only the initial encoding of the material had to be spatial and that once encoding was complete, the subject was probably only required to remember a static pattern of numbers in the matrix, not a spatial sequence. Logie and Marchetti predicted that the result might not be the same if the subject was genuinely required to retain a sequence of movements rather than a static pattern, as well as to recall a strictly visual sequence. Thus, in their experimental design the subject was required to retain information about either the sequential order in which a series of squares was presented at different locations on the screen or to remember colour hues. The retention interval was filled either by a concurrent movement task or irrelevant pictures. It was hypothesised that if separate systems are involved in retaining spatial and visual material then the movement task should disrupt memory only for the presentation sequence while the irrelevant pictures should only disrupt retention of the colour hues. This is what was found.
It should be noted that this finding does not say anything about whether or not the central executive is implicated in encoding. It does point to VSSP involvement in retention, however, and moreover provides evidence for separate cognitive systems being involved in the spatial and visual tasks. This is consistent with Logie (1989) who holds that the passive visual store would be responsible for retention of the colour hues and interference occurred because irrelevant visual input is thought to
have obligatory access to such a store. The rehearsal mechanism would be responsible for spatial recognition. As the control of movements is also involved with the rehearsal mechanism, the irrelevant movements disrupts the rehearsal mechanism.