Fast Learning of Simple Perceptual Discriminations Reduces Brain Activation in Working Memory and in High-level Auditory Regions Luba Daikhin and Merav Ahissar Abstract ■ Introducing simple stimulus regularities facilitates learning of both simple and complex tasks. This facilitation may reflect an implicit change in the strategies used to solve the task when successful predictions regarding incoming stimuli can be formed. We studied the modifications in brain activity associa- ted with fast perceptual learning based on regularity detection. We administered a two-tone frequency discrimination task and measured brain activation (fMRI) under two conditions: with and without a repeated reference tone. Although participants could not explicitly tell the difference between these two con- ditions, the introduced regularity affected both performance and the pattern of brain activation. The “No-Reference” condi- tion induced a larger activation in frontoparietal areas known to be part of the working memory network. However, only the condition with a reference showed fast learning, which was accompanied by a reduction of activity in the left intraparietal area, which is involved in stimulus retention, and in the posterior superior-temporal area, which is involved in representing audi- tory regularities. We propose that this joint reduction reflects a reduction of the need for online storage of the compared tones. We further suggest that this change reflects an implicit strategic shift “backwards” from reliance mainly on working memory net- works in the “No-Reference” condition to increased reliance on detected regularities stored in high-level auditory networks. ■ INTRODUCTION The dynamics of perceptual learning, particularly its ini- tial stages, are not well understood. Previous studies have focused on the specificity of learning to trained stimuli, which was shown to be consistent with the specificity of the sensory areas (Spang, Grimsen, Herzog, & Fahle, 2010; Van Wassenhove & Nagarajan, 2007; Amitay, Hawkey, & Moore, 2005; Seitz & Watanabe, 2005; Demany & Semal, 2002; Ahissar & Hochstein, 1993, 1996; Levi & Polat, 1996; Karni & Sagi, 1991). However, such speci- ficity mainly characterizes later stages of learning, when some expertise had been obtained ( Jeter, Dosher, Liu, & Lu, 2010; Ahissar & Hochstein, 1997; Karni & Sagi, 1993). Ahissar and Hochstein (Ahissar, Nahum, Nelken, & Hochstein, 2009; Ahissar & Hochstein, 1997, 2004) suggested that when finer resolution is required, per- ceptual learning may progress backwards along the per- ceptual hierarchy from crude generalizing representations to more local ones. This theory, termed the Reverse Hierarchy Theory, posits that perceptual learning is not limited to a specific brain site and progresses from high- to lower-level areas with practice. Nevertheless, it does not address the brain mechanisms underlying the very early stages of learning, when the task and its broad stimulus characteristics need to be sorted out. This initial stage is typically short and difficult to track and hence has rarely been studied, although it is probably crucial to subsequent learning dynamics (e.g., Ortiz & Wright, 2009; Hawkey, Amitay, & Moore, 2004; Karni, Jezzard, Adams, Turner, & Ungerleider, 1995). One of the key features of the training procedure, par- ticularly at the early training stages, is the consistency of stimuli across consecutive trials. Consistent training with similar stimuli leads to fast, condition-specific (Cohen, Daikhin, & Ahissar, 2013) learning (e.g., Otto, Herzog, Fahle, & Zhaoping, 2006), whereas training with a broad range of stimuli, whose sequence is not predictable, leads to slow learning (Parkosadze, Otto, Malaniya, Kezeli, & Herzog, 2008) if any (e.g., Kuai, Zhang, Klein, Levi, & Yu, 2005; Adini, Wilkonsky, Haspel, Tsodyks, & Sagi, 2004; Yu, Klein, & Levi, 2004). A very clear example of this dissociation was recently reported in the auditory modality for training on frequency (pitch) discrimination between sequentially presented tones. Whereas dis- crimination between tones whose frequency was ran- domly chosen from a broad frequency range improved slowly (within hundreds of trials), substantial and fast improvement was achieved when the first tone in a pair had a fixed frequency (Nahum, Daikhin, Lubin, Cohen, & Ahissar, 2010). This rapid improvement was attributed to the ability to form effective predictions for the incoming stimuli when training with stimuli that obeyed a simple regularity (Ahissar et al., 2009; Ahissar & Hochstein, 2004). Here we inquired whether the impact of intro- ducing simple regularities that facilitate learning, perhaps The Hebrew University of Jerusalem © Massachusetts Institute of Technology Journal of Cognitive Neuroscience X:Y, pp. 1–14 doi:10.1162/jocn_a_00786