New evidence for rapid development of colour–location binding in infants’ visual short-term memory

Abstract

Change-detection tasks reveal that infants’ ability to bind colour to location in visual short-term memory (VSTM) develops rapidly: Seven-month-old infants, but not six-month-old infants, detect that successive arrays of three objects are different if they contain the same colours in different locations (Oakes et al., 2006). Here we test a counterintuitive consequence of the hypothesis that 6-month-old infants are unable to bind colours to locations: When comparing two successive stimulus arrays, these infants will often compare noncorresponding items, making it impossible for them to distinguish between identical arrays and nonidentical arrays. As a result, they will not show a preference for changing arrays over nonchanging arrays even when all of the items change. We tested this prediction by presenting 6- and 7-month-old infants (N=36) with nonchanging displays of three items and changing displays in which all three items simultaneously changed colours. As predicted, 7-month-old infants, but not 6-month-old infants, responded to the difference between these changing and nonchanging displays, providing additional evidence that the ability to bind colours to locations develops rapidly across this age range.

Keywords:

• Infancy
• Visual short-term memory
• Binding

Acknowledgements

This research and preparation of this manuscript were made possible by NIH grant HD49840 awarded to LMO; SRS was funded by predoctoral and postdoctoral NRSAs (HD055040, MH068934). We thank Shaena Stille, Kristine Kovack-Lesh, and the undergraduate students in the Infant Perception and Cognition Laboratory at the University of Iowa for their help with this project.

Notes

¹One might expect that the individual 6-month-old infants would all have preference scores approximating .50. However, although most infants had scores near .50, a few had substantially higher or lower scores (see Figure 2). We examined the data of these infants carefully to see if we could find a clear explanation for their divergent scores, but we found no obvious differences between these infants and the infants whose scores were nearer to chance (e.g., they did not differ in age from the other infants and they generally looked at both streams on each trial). It is therefore likely that their divergent scores reflect measurement noise rather than true preferences for the changing or nonchanging streams.

²Substantial evidence supports the existence of separable short-term and long-term visual memory systems, which differ in terms of both their functional characteristics and their neural implementation (reviewed in Luck & Hollingworth, 2008). These systems may operate concurrently in many tasks that use relatively short retention intervals (< 10 s) but also use relatively long encoding periods (> 500 ms).

³It should also be noted that the pattern of performance exhibited by the 6-month-old infants in the experiments of Kaldy and Leslie (2003, 2005) is also consistent with infants simply remembering the identity of the last item shown, with no binding of identity and location.