The current results have replicated and extended Dent’s findings by showing the categorical advantage effect with different parameters,manipulated using the CATCOORD task.
Categorical changes result in better performance than coordinate changes, regardless of shift size or encoding time or retention interval of target. Importantly, in the shortest
encoding time, where it was assumed to be difficult to encode verbal categorical information in memory and participants were putatively forced to rely on non-verbal visual-spatial
information, categorical-change trials were still performed better than coordinate-change trials. In addition, when participants were assumed to rely on precise coordinate spatial representations for the smallest shift, categorical spatial changes were still easier to detect than coordinate spatial changes. In terms of retention interval, which has been
demonstrated to have an influence on the two spatial representations, categorical
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judgments were still found to be better than coordinate judgments. Specifically, in the shortest retention interval where verbal information was thought to be minimal and coordinate spatial attributes were heavily relied on in VSSTM, the categorical advantage effect was still found. Taken together, the present study demonstrated a difference between categorical and coordinate representations in visuospatial representations, with better performance for categorical than coordinate changes consistently observed. More
importantly, the findings support the notion of categorical spatial relations being an intrinsic property of encoding spatial arrays. When encoding and retention time were short and only non-verbal, visual-positional information was provided in the task, categorical spatial changes were still performed better than coordinate spatial changes.
The results replicated the previously found categorical advantage effect. Importantly, even with the manipulated encoding times, shift sizes, and retention intervals, which were designed to inhibit the formation of categorical representations, the categorical advantage effect was still found. Different from the findings of van der Ham et al. (2007), the current study did not demonstrate the sensitivity to different time courses for coordinate spatial relations. Several differences between their experiment design and the current design are illustrated in Table 2-1. The current experiment did not provide an explicit clue before spatial judgments and the stimuli were presented at the centre of the screen. These manipulations were designed to observe the two spatial representations without the characteristic of lateralisation. When participants were less likely to utilise verbal/categorical assistance to perform the task and had to heavily rely on iconic/coordinate related information, i.e. when the stimuli were presented rapidly (250ms) and retention interval was the shortest (500ms), a robust advantage of categorical over coordinate spatial relations was still found. The notion that the two spatial representations are sensitive to different time courses may only be applied when participants are explicitly instructed to make a certain spatial judgment and/or when stimuli are presented on a half visual field. Decay in memory performance associated with longer retention intervals illustrates a conventional phenomenon of many memory tasks. However, the fact that duration of encoding time did not affect participants’
performance may be due to a between-subject design.
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Table 2-1. Experiment design and methodology comparison between van der Ham et al. (2007) and the current experiment.
van der Ham et al. (2007) Experiment 1a Experiment paradigm A dot-cross task The CATCOORD task† Stimuli presentation Half visual field Whole visual field Explicit instructions
of spatial judgments Yes No
Encoding times Fixed (150ms)
Different (250ms, 500ms, 2500ms)
(N.B. between-subject variable)
Retention intervals Different (500ms, 2000ms, 5000ms)
Different (500ms, 2000ms, 5000ms)
Manipulation of shift sizes
Yes (4 possible positions in
each quadrant of the cross) Yes (15mm, 20mm, 25mm)
† As with Dent (2009)
It is suggested that the magnitude of shifts is an important factor in coordinate spatial representations. However, Dent (2009) aimed to distinguish categorical and coordinate spatial representations have only concentrated on categorical effects while other possible manipulations that may reveal the coordinate effects in VSSTM seem to have been omitted.
As the distances between target and reference in Dent’s work was fixed, the current study utilised a systematic manipulation of the distances between the targets and the references in order to explore categorical boundary in VSSTM. Minimal distance changes between objects may be outside of the categorical boundary and lead the categorical advantage effect to disappear in VSSTM. Moreover, the manipulation of subtle shifts between objects may benefit coordinate representations as they are sensitive to precise spatial changes. An identical colour of stimuli was used to provide limited information of objects’ identity and enhance spatial and positional features in the task. Participants may hence have had to rely on coordinate more than categorical spatial representations in trials with the smallest shift.
Nevertheless, judgments on categorical spatial relations were still performed better than those on coordinate spatial relations. That is to say, the role of categorical spatial
representations is dominant and coordinate spatial representations may be supplementary in VSSTM.
Verbal codes are seen as one of the attributes of categorical spatial representations. Dent (2009) conducted an experiment with an articulatory suppression task and found better
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performance in categorical than coordinate relations. Categorical changes were still more obvious than coordinate changes, even when one of their properties, the verbal component, was interrupted by articulatory suppression. Thus he deems that categorical representations are an immediate, intrinsic property in visuospatial representations. Moreover, van der Ham’s study (2007) showed that categorical spatial relations decayed less, even in longer retention intervals (2000ms and 5000ms). They suggested that longer retention intervals might provide opportunities for participants to apply a more verbal memorisation strategy, which assisted for categorical representations. The maintenance interval (2 seconds) applied in Dent’s study may have already created a bias in favour of categorical spatial
representations. Before concluding that verbal information is an intrinsic property of categorical spatial representations in visual spatial configurations, further examinations on the two subunits of categorical representations in VSSTM are required.
In sum, Experiment 1a has replicated the findings by Dent (2009) and showed a consistent categorical advantage throughout various experiment parameters with the CATCOORD task.
The contribution of categorical representations is salient in visuo-spatial relations even when the visual capacity is forced to extremes (e.g. 250ms presentation time of the stimuli) or in conditions where categorical information is minimal (e.g. 15mm shift of the targets).
2.3 Experiment 1b: CATCOORD task with unicolour, with/without auditory