JSLHR Review Article Cortical and Sensory Causes of Individual Differences in Selective Attention Ability Among Listeners With Normal Hearing Thresholds Barbara Shinn-Cunninghama Purpose: This review provides clinicians with an overview even in listeners with NHTs. Studies of variability in control of of recent findings relevant to understanding why listeners attention and in sensory coding fidelity may help to isolate with normal hearing thresholds (NHTs) sometimes suffer and identify some of the causes of communication disorders from communication difficulties in noisy settings. in individuals presenting at the clinic with “normal hearing.” Method: The results from neuroscience and psychoacoustics Conclusions: How well an individual with NHTs can are reviewed. understand speech amidst competing sounds depends Results: In noisy settings, listeners focus their attention by not only on the sound being audible but also on the engaging cortical brain networks to suppress unimportant integrity of cortical control networks and the fidelity of the sounds; they then can analyze and understand an important representation of suprathreshold sound. Understanding sound, such as speech, amidst competing sounds. Differences the root cause of difficulties experienced by listeners with in the efficacy of top-down control of attention can affect NHTs ultimately can lead to new, targeted interventions that communication abilities. In addition, subclinical deficits address specific deficits affecting communication in noise. in sensory fidelity can disrupt the ability to perceptually Presentation Video: http://cred.pubs.asha.org/article. segregate sound sources, interfering with selective attention, aspx?articleid=2601617 This research forum contains papers from the 2016 Research The challenge of understanding speech in settings Symposium at the ASHA Convention held in Philadelphia, PA. where there are multiple sound sources is known as the n a sizeable minority of cases, patients seeking audio- cocktail party problem, a term originally coined by Cherry logical treatment have normal hearing thresholds (1953). Understanding how listeners with normal hear- (NHTs) but report difficulties understanding speech ing solve the cocktail party problem has remained a focus I of study for over 50 years (e.g., see Bee & Micheyl, 2008; when there are competing sound sources (Hind et al., 2011). Such listeners are said to have “central auditory process- Bodden, 1993; Hafter et al., 2013; Wood & Cowan, 1995; ing disorder” or “auditory processing disorder” (Furman, Yost, 1997), in no small part because of its importance: Kujawa, & Liberman, 2013; Kujawa & Liberman, 2009; Lin, difficulties in such settings expose communication difficul- Furman, Kujawa, & Liberman, 2011; Rosen, Cohen, & ties that do not show up in simpler listening conditions. Vanniasegaram, 2010), a catchall diagnosis that says nothing There are numerous reasons why listeners with NHTs about the underlying causes of the communication diffi- might find it difficult to communicate in noisy environ- culties, making it difficult to develop effective treatments. ments, from language-specific deficits to general cognitive deficits. This article reviews two specific issues that can affect the ability of listeners with NHTs to solve the cock- tail party problem: (a) efficacy of cognitive control net- works in the brain responsible for focusing selective auditory aCenter for Research in Sensory Communication and Emerging Neural Technology, Boston University, MA attention and (b) fidelity of the sensory representation of suprathreshold (clearly audible) sound. By differentiating Correspondence to Barbara Shinn-Cunningham: [email protected] among more specific mechanistic failures that can impede Editor-in-Chief: Frederick (Erick) Gallun Editor: Karen Helfer communication in complex settings, clinicians will be able Received February 27, 2017 Revision received June 23, 2017 Accepted July 5, 2017 Disclosure: The author has declared that no competing interests existed at the time https://doi.org/10.1044/2017_JSLHR-H-17-0080 of publication. 2976 Journal of Speech, Language, and Hearing Research • Vol. 60 • 2976–2988 • October 2017 • Copyright © 2017 American Speech-Language-Hearing Association Research Forum: Advances in Research on Auditory Attention and the Processing of Complex Auditory Stimuli Downloaded From: http://jslhr.pubs.asha.org/ by a Boston University User on 10/19/2017 Terms of Use: http://pubs.asha.org/ss/rights_and_permissions.aspx to provide appropriate counseling and care management This inability to process everything in a scene enables and, ultimately, targeted interventions. a skilled magician to astonish us with her sleight of hand; At first, it may seem surprising that listeners can have by drawing our attention to some salient, engaging event, difficulty understanding speech in cocktail party settings such as a dramatic flourish of her cape, we miss how she but do not report difficulty in other listening situations. drops the “disappearing” coin into her pocket. In a com- However, solving the cocktail party problem places much plex scene, we naturally focus on an object that is interest- greater cognitive and sensory demands on the listener ing, either because it is inherently important (such as the than does listening in quiet. As discussed in the section on sight of a lone person in an empty restaurant or the sound We Rely on Selective Attention to Communicate in Noisy of a voice amidst buses and cars on a busy street) or be- Social Settings, audibility often is not the factor that limits cause it is surprising (such as an unexpected flash of light- understanding for listeners with NHTs. Instead, central ning or a sudden clap of thunder). In the laboratory, our processing resources can limit what we can consciously per- poor ability to identify changes in complex visual or audi- ceive. We manage this limitation by focusing attention on tory scenes—especially when the change is in some “boring” whatever acoustic source we will process, which relies on background detail—is known as either “change blind- engaging cortical networks to filter inputs in ways that are ness” (e.g., see Beck, Rees, Frith, & Lavie, 2001; Rensink, unnecessary in quiet. Some listeners may have problems 2002; Simons & Levin, 1997; Simons & Rensink, 2005) controlling cortical control networks and, therefore, have or “change deafness” (e.g., see Dalton & Fraenkel, 2012; difficulty focusing selectively on whatever sound they want Eramudugolla, Irvine, McAnally, Martin, & Mattingley, to hear, an idea developed further in the section Individuals 2005; Koreimann, Gula, & Vitouch, 2014), respectively. Ex- Differ in Their Ability to Control Selective Attention. More periments investigating change blindness and change deaf- important, as discussed in the section on Auditory Selective ness provide controlled laboratory demonstrations of the Attention Depends on Auditory Object Formation, selec- idea that, unless we actively attend to sensory informa- tion of a sound source from a mixture of competing sounds tion that is readily available on the retina or the cochlea, can only be effective if we are able to perceptually segregate we will fail to consciously perceive that information. Change the sources in the sound mixture reaching our ears, a pro- blindness and change deafness prove that we do not pro- cess known as auditory scene analysis (Bregman, 1990). The cess every bit of information available to us; instead, atten- ability to analyze and make sense of an auditory scene de- tion governs a bottleneck in our perceptual processing, pends upon the sensory representation of the acoustic mix- determining what we “see” and “hear” from the informa- ture being robust and rich enough to support perceptual tion assailing our eyes and ears. segregation. Critically, as discussed in the section on Indi- What object a listener (or viewer) attends is not sim- viduals Differ in Their Ability to Encode Fine Temporal ply determined by top-down intention (focusing on some- Details in Suprathreshold Sound, even listeners with NHTs thing we think is important, behaviorally). Instead, there is may suffer from sensory deficits that impair auditory scene a complex interplay between volitional focus and bottom-up analysis. salience (Desimone & Duncan, 1995; Kastner & Ungerleider, The outcome of having difficulty when trying to 2001). Specifically, sudden, unexpected events can draw understand speech in noisy settings may be caused by very attention involuntarily, no matter what one’s intention; for different underlying causes. As discussed in the section instance, if you are trying to listen to your date at a loud Future Impact in the Clinic, there are no effective treatments restaurant and the waiter drops a tray behind you, your yet for these issues; however, as we begin to understand attention will be drawn to the crash of the glass and china the mechanisms that can lead to difficulties communicat- at your back. Regardless of whether the sound that is ing in noise, specific interventions and treatments can be attended to is something you were trying to hear or some- developed. thing that grabbed your focus involuntarily, the result is the same: once you are focused on one sound, other sounds outside the focus of attention are processed with less detail. We Rely on Selective Attention to Attention Modulates What Information Communicate in Noisy Social Settings Is Encoded in Sensory Cortical Regions Selective Attention Determines What