Six pigeons were trained in a change detection task with four colors. They were shown two colored circles on a sample array, followed by a test array with the color of one circle changed. The pigeons learned to choose the changed color and transferred their performance to four unfamiliar colors, suggesting that they had learned a generalized concept of color change. They also transferred performance to test delays several times their 50-msec training delay without prior delay training. The accurate delay performance of several seconds suggests that their change detection was memory based, as opposed to a perceptual attentional capture process. These experiments are the first to show that an animal species (pigeons, in this case) can learn a change detection task identical to ones used to test human memory, thereby providing the possibility of directly comparing short-term memory processing across species.
Memory typically requires storage, processing, and retrieval of information. Although memory research has been avidly pursued for more than a century, characteristics of different kinds of memory continue to be discovered at an ever increasing pace. Short-term memory is the foundation of long-term memory but is typically thought to be limited in terms of storage capacity or durability. One of the most popular procedures for studying shortterm memory in humans has been change detection. For example in one change detection study, several objects (e.g., colored squares) were presented in a sample array, and after a short delay, subjects identified which object in a test array had changed (e.g., Eng, Chen, & Jiang, 2005). Although animals have not previously been tested in change detection, this procedure should be eminently suitable for testing animal short-term memory and making direct species comparisons, because change detection does not depend on verbal memory (e.g., Alvarez & Cavanagh, 2004; Luck & Vogel, 1997).
Change detection differs from other animal memory testing procedures, such as the matching-to-sample (MTS) or same/different (S/D) procedure. Human experiments have shown change detection to be fundamentally different from visual search, which is equivalent to a delayed MTS procedure (Eng et al., 2005). Rensink (2002) reviewed change detection and compared it with S/D performance, saying that "the two [change detection and S/D] are not the same" and that change detection is a temporal transformation resulting in dynamic change, whereas S/D involves "no notion of transformation" (p. 250). In change detection, transformation depends on recognizing that the two object arrays (i.e., sample and test arrays) are related. Perhaps critical to this concept of transformation is that the test objects are presented in the same locations as the sample objects. Same locations provide a no-change context, so that the two object arrays can be more easily related and the concept of transformation and change may be more easily learned.
In the experiments reported in this article, we trained and tested pigeons in a change detection task that required them to detect the changed item in a test display. Our change detection procedure was modeled after that used by Eng et al. (2005), and similar procedures have been used by other researchers to test human memory (e.g., Hollingworth, 2007; Mondy & Coltheart, 2006; Smilek, Eastwood, & Merikle, 2000). The procedure of identifying which item has changed yields results (e.g., visual working memory capacity) similar to those for procedures of reporting whether or not a change has occurred (cf. Alvarez & Cavanagh, 2004). A consideration for adopting the procedure requiring pigeons to respond to the changed item was that animals generally attend better to stimuli they touch or peck and, thereby, learn more rapidly (e.g., Harrison, Iversen, & Pratt, 1977; Stollnitz, 1965; Wright, Shyan, & Jitsumori, 1990). In addition, as Green and Swets (1966) pointed out more than 40 years ago, forced choice psychophysical procedures (e. …