Implicit recognition based on lateralized perceptual fluency.

Brain Sci. 2012, 2, 22-32; doi:10.3390/brainsci2010022 OPEN ACCESS brain sciences ISSN 2076-3425 www.mdpi.com/journal/brainsci/ Article Implicit Recognition Based on Lateralized Perceptual Fluency Iliana M. Vargas 1, Joel L. Voss 2 and Ken A. Paller 1,* 1 2 Department of Psychology, Northwestern University, Evanston, IL 60208, USA; E-Mail: Department of Medical Social Sciences, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA; E-Mail: * Author to whom correspondence should be addressed; E-Mail: ; Tel.: +1-847-467-3370; Fax: +1-847-467-1329. Received: 20 December 2011; in revised form: 21 January 2012 / Accepted: 31 January 2012 / Published: 6 February 2012 Abstract: In some circumstances, accurate recognition of repeated images in an explicit memory test is driven by implicit memory. We propose that this “implicit recognition” results from perceptual fluency that influences responding without awareness of memory retrieval. Here we examined whether recognition would vary if images appeared in the same or different visual hemifield during learning and testing. Kaleidoscope images were briefly presented left or right of fixation during divided-attention encoding. Presentation in the same visual hemifield at test produced higher recognition accuracy than presentation in the opposite visual hemifield, but only for guess responses. These correct guesses likely reflect a contribution from implicit recognition, given that when the stimulated visual hemifield was the same at study and test, recognition accuracy was higher for guess responses than for responses with any level of confidence. The dramatic difference in guessing accuracy as a function of lateralized perceptual overlap between study and test suggests that implicit recognition arises from memory storage in visual cortical networks that mediate repetition-induced fluency increments. Keywords: implicit memory; recognition; perceptual priming Brain Sci. 2012, 2 23 1. Introduction Recognition is the ability to correctly identify a previously experienced stimulus as such and is normally considered a hallmark of explicit memory. Explicit memory refers to the ability to consciously recognize or recall previously experienced information. In contrast, implicit memory refers to various other instances when stored information influences behavior without awareness of memory retrieval. For example, perceptual implicit memory for visual stimulus features can be shown by faster and more accurate responses in a perceptual priming test and is believed to occur through repetition-induced fluency of perceptual processing within visual cortex [1,2]. Specific neural mechanisms that might underlie repetition-induced fluency are currently under active debate [3]. A related controversy concerns the extent to which this repetition-induced fluency contributes to explicit memory as commonly assessed in a recognition test. Jacoby’s [4] process-dissociation methodology presented an alternative to contrasting implicit memory tests with explicit memory tests. He argued that a combination of automatic and intentional processes contribute to memory performance, and that memory tests do not provide pure measures of one or the other type of process. Applied to results from recognition testing, the process-dissociation methodology represents an attempt to separate the contribution of these different processes. This tactic thus acknowledges the idea that an explicit memory test can engage an automatic component of performance (perhaps related to implicit memory). Evidence consistent with the idea that recognition responses can be driven by implicit-memory processes akin to those thought to support perceptual priming can be seen in various applications of the process-dissociation methodology as well as in a variety of other experimental protocols (e.g., [5–8]). Influences of relatively automatic processing (e.g., perceptual fluency) on recognition performance may be greatest when semantic elaboration is minimal [9] and when explicit memory is weak [10,11]. Indeed, a direct influence of manipulations of perceptual fluency has been observed in various studies of recognition (e.g., [12–14]). Also, superior memory for stimuli studied and tested in the same versus a different modality in both explicit and implicit memory tests has been attributed to similar processes operating in both types of test [15]. On the other hand, other results suggest that perceptual fluency does not contribute to recognition decisions (e.g., [16,17]). Most dramatically, some amnesic patients can achieve only chance levels of recognition accuracy but also exhibit normal implicit memory for the same stimuli on various priming tests [18,19]. Given that implicit memory was operative at normal levels in these amnesic patients, a reasonable conclusion is that implicit memory does not contribute to recognition, because if it did then recognition performance should have been above chance. The controversy about whether implicit memory can or cannot support recognition performance seems tied to settling on a general answer to this question. As opposed to an all-or-none orientation, however, the question might best be framed by asking whether certain circumstances promote accurate recognition driven by perceptual fluency without awareness of retrieval, which we have termed implicit recognition. In other words, to settle this controversy it may prove helpful to identify task and stimulus parameters that promote implicit recognition, which would open the door to considering the degree to which implicit recognition may be operative in various circumstances. In a recognition test, implicit recognition may occur on an unknown subset of trials. In order to obtain convincing evidence demonstrating implicit recognition, it must occur reliably on a large Brain Sci. 2012, 2 24 number of trials. In a series of studies, we therefore used stimulus and task parameters that we thought would maximize implicit recognition. We also made use of confidence judgments, such that a lack of confidence (i.e., a guess) would be one way to indicate a lack of awareness of retrieval. Although these metamemory judgments might be subject to various biases and may not always be veridical, consistently different findings for guesses and confident recognition responses can be highly informative. We obtained our initial evidence for implicit recognition using forced-choice tests of recognition memory for previously seen kaleidoscope images [20–22]. These stimuli tend to provoke very little conceptual processing, though some color naming may occur during learning. However, the same colors were used in to-be-learned stimuli and in foil stimuli presented during recognition testing, such that memory for color names was seldom diagnostic during a test. Successful recognition was thus heavily based on visual features. A key manipulation that produced results implicating implicit recognitio (...truncated)