Balancing Perception and Cognition in an Attention-Centric Cognitive System Anon Y. Mous Abstract That flexible, intelligent, goal-directed behavior in a dynamic world requires heuristic computation has been widely appreciated since the early days of artificial intelligence and cognitive science. Ultimately, all heuristics share the property of being “selective” with respect to a space of options. In (biological) cognitive systems, attention is often billed as the mechanism that manifests this selectivity. Attention is thought to be a part of a larger cluster of mechanisms that serve to orient a cognitive system, to filter contents with respect to their task relevance, and to devote more computation to certain options than to others. All these activities proceed under the plausible assumption that not all information can be or ought to be processed for a system to satisfice in an ever changing world. In this paper, we describe an attention-centric cognitive system called ARCADIA that demonstrates the orienting, filtering, and resourceskewing functions mentioned above. The demonstration involves maintaining focus on a simple cognitive task (i.e., counting certain perceptual events) in a dynamic environment. While the system successfully carries out the task, limits on attentional capacity result in“inattentional blindness” under circumstances analogous to those where people show similar behavior. Introduction Flexible, intelligent behavior in a dynamic world requires cognitive systems that strike a balance between reactivity and high-level cognition. In the biological realm, selective attention is often invoked as the means by which this balance may be struck. Attention is under our willful control when we concentrate on a task at hand and can be captured by highly salient stimuli like the sound of our name being shouted by a friend. The interplay between focused attention and attentional capture is complex. When people are involved in a task, the presence of too many highly salient, task-irrelevant stimuli leads to degraded performance. Conversely, too much concentration on a particular thought or task may lead to failures in noticing what would otherwise be a highly salient (and perhaps important) stimulus. To illustrate these failures, consider the case where a driver is texting and fails to see the police car parked a few meters ahead, recall trying to understand your friend over the phone while standing in a noisy room, and reflect on being “in the zone” while programming or writing and forgetting to eat. As these examples show, success in the world involves being able to strike an effective balance between being reactive and being task focused. Perhaps striking that balance involves reminding oneself to ignore the mobile phone while driving or to set an alarm while coding as a way to enforce breaks. Both of these strategies help control attention in situations where, possibly, one has experienced a failure in the past and seeks to avoid them in the future. This paper describes a cognitive system that balances perception and cognition using strategies of this sort. The system is predicated on the idea that attentional strategies, both learned and innate, serve to coordinate perception and cognition. Given attention’s central role throughout human cognition, the limited treatment in the cognitive systems literature is disconcerting. To be sure, researchers within this field have addressed certain aspects of attention, perception, and cognition, but rarely has their intersection been explored. One one side of a coin, the vast majority of computational work on vision and especially on object recognition is massively implausible from a psychological perspective.1 The copious amount of labeled training data and brute-force image processing strategies employed in those efforts are at odds with both common sense and the deliverances of vision science. On the other side of the coin, psychologically plausible approaches to perception in some of the betterknown cognitive architectures such as ACT-R (Nyamsuren and Taatgen 2013) and EPIC (Kieras 2010) rely on symbolic encodings of objects, relations, and events. There seems to be an empty space between these two families of research approaches: a space for systems that operate over real sensor data, but do so in psychologically plausible ways. An attention-centric cognitive system may both exhibit perceptual selectivity in image processing and provide a theorygrounded platform for exploring the perception–cognition interface. Minding the Gap The plan for the rest of the paper is as follows. First, we introduce an attention-centric cognitive system called ARCADIA, which stands for Adaptive, Reflective Cognition in an Attention-Driven Integrated Architecture. To demonstrate how the architecture can combine top-down (i.e., cognitive) and bottom-up (i.e., perceptual) factors, we describe work to date on a visual pipeline in ARCADIA. Bridewell and Bello (2015) previously applied this pipeline to a change detection task and provided details on the how these factors determine where the system focuses its attention. Importantly, 1 We have no particular opinion about the utility of high fidelity, psychologically plausible models in creating artificial, cognitive systems. In our view, psychologically implausible approaches may well be on the right track and the comments we make here should not be taken as impugning those approaches. Internal Identifier ID Name Arguments World Source Type The element's variadic relation Map from a relation's argument names to objects Named collection of elements that belong to a distinct perspective Component that produced the element Class of the element's relation Figure 2: A schema for encoding an element in ARCADIA’s interlingua. Figure 1: ARCADIA’s tripartite informational structure (top), and its cognitive cycle (bottom). under certain, psychologically plausible conditions the architecture exhibited change blindness which is a surprising, human insensitivity to dynamism in the world (Simons and Rensink 2005). After providing a walkthrough of ARCADIA’s visual pipeline in the change-detection task, we report on ARCADIA’s ability to carry out the cognitive task of counting the number of times that a moving ball changes color. This time we find that under certain conditions ARCADIA exhibits inattentional blindness, a psychological phenomenon where people fail to recognize otherwise salient stimuli when their attentional capacities are taxed. Here, a stimulus engineered to provide a strong bottom-up saliency signal is ignored as the system pursues its counting task. Importantly, when ARCADIA is not tasked with counting, its attention moves between the ball on the screen and the other salient stimulus that was previously ignored due to limits on attention. Finally, we explore trade-offs at the perception–cognition interface; especially the idea that one could increase attentional capacity in artificial cognitive systems and hope to mitigate the unwanted side-effects of these limitations. The ARCADIA Cognitive System ARCADIA embodies a theoretical commitment to attention as a central, integrating mechanism for perception, cognition, and action. The system operates in distinct cognitive cycles that are guided by a focus of attention. In terms of intellectual roots, ARCADIA shares much of the structure found in the Global Workspace Theory of consciousness (Baars 1997). This connection should come as no surprise: the relationship between attention, perception, and consciousness has generated an enormous amount of literature over the years and continues to be a fruitful area of research (Koch and Tsuchiya 2012; Dehaene et al. 2006). As shown in the top of figure 1, ARCADIA’s general structure is tripartite, consisting of components, accessible content, and the aforementioned focus of attention, each of which will be described in detail as our discussion proceeds. Note that ARCADIA makes a principled distinction between aspects of cognition that are and are not able to be introspected or verbally reported.2 Figure 1 illustrates this distinction with uninspectable processing occurring at the bottom in the activity of the system’s components, and potentially inspectable, reportable representations and activity (more accurately, representations of activity) contained in the middle and upper parts of the pyramid. Representation in ARCADIA Representation in ARCADIA is multifarious and differs between its inspectable and uninspectable layers. Components, which are computational modules, encapsulate low-level processes. ARCADIA places no theoretical restrictions on the representational format or processing characteristics for components in general, although one may develop components that reflect theoretical positions. This freedom at the system level enables flexibility in design. Components can employ any sort of data structures and algorithms, including but not limited to neural networks, production rules, graphical models, frames, or constraint graphs, letting modelers use whatever solution best fits the task at hand and trade it for a better one when available. Similarly, the data processed within components is equally unconstrained. Multidimensional matrices for images, waveforms for sounds, symbolic structures for propositional and relationally structured data are all admissible. Interlingua ARCADIA is an integrated architecture, so components with disparate representational formats must communicate with each other. To this end, each component interfaces with accessible content and the current focus of attention through an interlingua. Figure 2 provides a schema for an element expressed in the interlingua. Each element consists of a unique identifier, a variadic argument-list, and a symbolic name for the collection of arguments. The arguments contain labeled data produced by the components and stored in formats that they can process. As a result, the interlingua can bind visual, auditory, and other sensory data to abstract, symbolically represented content retrieved from long-term memory structures. Moreover, each element tracks which component produced it by way of a source tag 2 The conscious–unconscious distinction does not quite work here. Most memories are unconscious because they are inactive and are not poised to be used in inference. Inactivity does not entail an inability to become conscious or otherwise usable in inference. and has type (e.g., action-description or object-instance). Finally, interlingua elements are indexed to worlds, which describe the situation that each element refers to. For instance, elements describing aspects of ongoing perception are assigned the world “reality” whereas interlingua elements corresponding to mental simulations of fictional, hypothetical, or counterfactual worlds would have a world argument corresponding to the name for the respective simulation. Components and Inference Although not shown explicitly in figure 1, there are three distinct classes of components in ARCADIA. The first kind of component polls sensor data. When a sensory input channel is established for ARCADIA (e.g., a video, a soundscape), this class of components samples the input channel and passes the sample to the second class of components: those that operate directly on sensory data. For the case of video processing, ARCADIA’s video-polling component samples a frame in the form of a matrix of image data and hands it to one or more components that operate directly on sensory data (examples to follow). After these low-level (i.e., close to sensory input) components complete their processing, they encode their results in interlingua elements and deliver them to ARCADIA’s middle layer where they may be used by other components. Finally, all other components implement routines that scan ARCADIA’s middle layer for the particular type of contents they are specialized to process, extract data from the arguments in the elements, carry out relevant processing over the extracted data, and encode results into new interlingua elements that are pushed up into the middle layer. Accessible Content and the Focus of Attention The top of figure 1 indicates that ARCADIA maintains a separate space called accessible content. This area stores ephemeral representations produced each cycle by low-level components. In here, the system makes available the contents of working memory, the results of perceptual processing, and other potentially reportable information. Similar to Baars’ concept of the global workspace, accessible content is substantially larger than working memory, and we take as an assumption, subject to revision, that it corresponds to the informational contents of consciousness.3 Elements in this space result from the attentional process that drives ARCADIA’s cognitive cycle and are produced by components as they respond to the focus of attention or sensory input. Notably, the theoretical relationship between accessible content and consciousness implies that verbal report is limited to the items that accessible content contains. As we have stated, ARCADIA maintains a focus of attention. Operationally, the focus of attention is a privileged element of accessible content that the system broadcasts to 1. Change Event 2. Action Request 3. New Objects 4. Fixation Request 5. Candidate Fixation 6. Random Element Task Specific Components Task General Components Figure 3: Attentional strategy for change detection. the components,4 represented by the downward arrow in figure 1. As a result, the focus has the power to alter the direction of processing within the system, enabling shifts from top-down, deliberative control to bottom-up, sensory responsiveness and back. Note that the focus itself does no inferential or perceptual work, rather it influences behavior in the system indirectly. Only those (non-sensory) components responsive to the information in the focus will be active during a cycle, and they will therefore produce the focus of attention and accessible content for the next cycle. The Cognitive Cycle and Focus Selection The bottom of figure 1 illustrates ARCADIA’s cognitive cycle. On each iteration, low-level components receive the current focus of attention and may query accessible content produced during the previous iteration. Designated pre-attentive components connect directly to sensory systems such as cameras, while others operate over only the focus and accessible content. Components automatically engage in processing and run to completion if they find input that they can respond to. The architecture deposits interlingua elements that are produced by components into what will become the next cycle’s accessible content and that may become the next focus of attention for the system. The structure, function, and properties of the elements vary. Some components produce bound object or event representations, whereas others produce abstract output, such as an expectation, whose arguments refer to other interlingua elements. The only place where processing occurs outside of components is during focus selection. The focus selector is an architectural mechanism that uses an attentional strategy to choose the next focus of attention (see figure 3). Such strategies serve as control knowledge for how to pursue a task. In principle, attentional strategies can be a function of arbitrary complexity, but we currently use priority lists that prefer one set of elements over others. For instance, one may specify that the system should consider focusing on an available action request before focusing on a representation of an object. In the next section, we describe an instantiation of a visual pipeline in ARCADIA and trace through its computations as the system constructs object representations. This process occurs over multiple cycles, begins with raw image data, and typically produces an element that is stored in visual short-term memory. In parallel, the system continues to 3 If one accepts the distinction between access consciousness and phenomenal consciousness as championed by Ned Block (1995), ARCADIA’s middle layer roughly corresponds to the former. Accessible content comprises elements poised for use in inference or verbal report. 4 Even though the focus is limited to a single element, the interlingua allows substantial internal structure in the argument list and the focus is supported by the contextual information in accessible content. vSTM Identity Round, Red, Circle Focus of Attention (Partial Illustration) Currently Active Attentional Strategy !!! Round, Red, Circle NEW !!! • In region X: Round, Red, Circle... Bottom-Up Feature Computation Iconic Memory Bottom-Up Fixation Generation Top-Down Fixation Generation vSTM Early Binder Round, Red, Circle Early Binder Property Detectors Figure 4: Processing during a model of vision in ARCADIA. process sensor data, and the resulting elements may capture attention, thereby disrupting the construction of an object representation. • Change Detection in ARCADIA The initial version of ARCADIA’s visual pipeline was designed for object localization, identification, and tracking, but with minor extensions, it can also detect changes in one or more properties of an object. To this end, the attentional strategy reflects priorities both for constructing objects from visual data and for the task of detecting (visual) changes in objects in the world. ARCADIA differs from most cognitive architectures in that it operates over pixel-level, video data. Further, the system takes multiple cycles to construct object representations from low-level features (e.g., closed contours, color profiles, “retinal” location). Once constructed, the representations must be tagged as referring either to new object instances or to previously seen objects. Because objects take multiple cycles to encode into representations, interruptions in the normal object-construction process may result in errors that are characteristic of human perception, which we discuss in the next section. As shown in figure 4, ARCADIA’s visual pipeline is served by a variety of components. Space precludes discussing the computational details of each component, however we give succinct descriptions below. • Bottom-Up Feature Computation polls a camera component for the current frame of visual input. Feature computation is carried out by an implementation of the Itti-Koch approach to visual saliency calculations (Itti, Koch, and Niebur 1998). The output of this component is an interlingua element that has a visual saliency map and the point of maximum bottom-up saliency in its argument list. • Iconic Memory also takes frames directly from a camera component. These frames are segmented to extract closed contour regions from the image along with location and hue-saturation-value information. The output of iconic memory is an interlingua element that has a list of protoobjects (Rensink 2000), one for each detected closed contour, with associated location and hue-saturation-value information. • Bottom Up Fixation Generation produces requests for visual foveation guided by attention capture. This com- • • • ponent scans accessible content for proto-objects and saliency maps and attempts to find the maximally salient proto-object. The resulting region containing that protoobject is encoded as a fixation request and passed to accessible content. Top Down Fixation Generation also produces foveation requests, but it is guided by the task at hand. In this case, the task is change detection, which plausibly involves reexamining objects for alterations to their properties. This component scans accessible content for elements of visual short term memory (vSTM) and requests fixations at the last-reported location of one of these (currently selected at random). As with the bottom-up component, the resulting region is encoded and passed to accessible content. Early Binder responds to a fixation in the focus of attention. This component takes the proto-object target of that fixation and stores it for one extra cycle. Simultaneously, various property detection components (classifiers for color, shape, etc.) produce classifications that are delivered to accessible content. In the next cycle, early binder scans accessible content for these classifications, gathers the positive instances and creates a new interlingua element that represents the object, populating the argument list with the positive classifications. The new object representation is passed to accessible content. Identity responds to an object representation in the focus of attention and determines whether the object was previously encountered. This task is carried out by scanning accessible content for other objects that were previously encoded item in vSTM. For this particular implementation, the identity component checks to see if the new object is the same size and at a spatial location within a small threshold with respect to the vSTM items in accessible content. If so, the identity component produces an interlingua element that marks the object as being an update, and if not, marks it as new. Visual Short Term Memory scans accessible content on each cycle for interlingua elements produced by the identity component. When it encounters an interlingua element marked as new, it inserts the element into its list. Updates are handled by finding the closest existing element in its list, and updating property values. Internally, vSTM is capacity-limited at six objects. On each cycle, vSTM outputs each of its object representations into accessible content. Change Detection (not pictured) is a task specific component that looks for color differences. This component examines elements in accessible content for identity relationships between old and new objects (along size and location dimensions) that differ in color and produces an element that stores the old and new state of the object, representing the detection when a discrepancy is found. Other components in ARCADIA include a change reporter that spots changes in the focus of attention and outputs the discovery, a working memory that stores change events among other things, and modules for moving cameras and monitoring fixations. Attention and Failures to Perceive The hybrid attentional strategy for change detection and object construction is shown in in figure 3, and duly prioritizes reporting changes when they appear in accessible content. If no changes are found, then the focus is given to new objects. If there are no changes or new objects, ARCADIA will focus on (accepted and processed) fixation requests, then candidate fixations, and finally on a random element. Because certain components involved in early vision operate independently from the focus of attention, fixation candidates are generated in parallel alongside feature-binding and encoding. While this is usually an unproblematic sequence, certain forms of perceptual interruptions can occur, as they do in change blindness. Change Blindness in ARCADIA Change blindness is a perceptual phenomenon wherein large visual changes occurring in full view go unnoticed (Simons and Rensink 2005). In a typical change blindness experiment, subjects view an initial image followed by a fleeting disruption in visual continuity: an blank screen, localized blotches superimposed on the image, or short film-cuts (on the order of tens of milliseconds), during which time the image is modified in some way. When visual continuity resumes, subjects can only rarely identify where the change occurred. Researchers conjecture that disruptions occurring across the whole of the visual field nullify the ability of bottom-up saliency calculations to guide attention to the region where the alteration occurs. For a detailed walkthrough of change blindness in ARCADIA, see the work by Bridewell and Bello (2015). Inattentional Blindness in ARCADIA Whereas change blindness embodies a failure of bottom-up attentional capture, a top-down, strategic focusing of attention may also lead to failures to perceive. Inattentional blindness is one particularly well known instance of the latter phenomenon that results from capacity limitations on the focus of attention. Research on inattentional blindness suggests that people consciously experience only those objects and events to which they directly attend (Mack and Rock 1998). As such, failures to attend entail failures to consciously experience, and corresponding failures to verbally report. Because attentional focus is widely considered to be extremely limited, strategic focus on one particular task or aspect of the environment leaves the perceiver open to missing much of what is going on around them. In a poignant demonstration, Hyman and colleagues found that subjects involved in a conversation on their mobile phones while walking through a park failed to notice a unicycling clown along their route (Hyman et al. 2010). Notably, inattentional blindness is not an all-or-none phenomenon. The degree to which perceivers are unaware of a particular stimulus depends on a variety of factors: most notably its visual similarity to the current focus and its relative distance from the object or event on which the focus of attention is currently trained (Most et al. 2001; Newby and Rock 1998). We predict that because ARCADIA is equipped with a limited focus of attention, it too should fall prey to inattentional blindness when strategically focused on a particular object or task. To this end, we designed a video stimulus comprising a single ball that moves on a white background and occasionally changes direction. While moving, the ball also changes from blue to green multiple times. ARCADIA’s task is to count the number of times that the ball changes color. During the video, a highly salient stimulus, a bright red star, zips across the bottom of the display. Because ARCADIA’s attention is trained solely on the ball for purposes of tracking and counting color changes, we predict that attention will never be captured by the red star, even though it may be pre-attentively processed by certain components (bottom-up feature detection, iconic memory, etc.). Accordingly, we predict that removal of the counting task will result in ARCADIA’s attention flickering back and forth between the star and the ball. To be clear, ARCADIA does not have explicit goals or established task structures at this time. Modeling a task in the system involves implementing components that provide the required functionality and an attentional strategy that can produce the desired behavior. For counting color changes, we start with the model of change detection that we described earlier in the paper. To this, we add two components: working memory and a change counter. The attentional strategy resembles the one in figure 3 with an added distinction. We discuss these efforts before discussing the resulting system behavior. Added Components: Counting and Remembering • Working Memory provides storage for information that is actively used by the system, operating like a cache. This component responds to memorization requests, which have type “action,” in the focus of attention. These may take the form of “remember this new element” or as updates of the form “replace an earlier version of this element with this new one.” As with vSTM, working memory makes its elements available as accessible content. • Change Counter responds to a change event in the focus of attention. To this end, the component looks for a number associated with counting changes in accessible content. If there is no such number, the change counter produces a request to memorize the number one, with the properties that it is a “counter” and that it updates on a “change.” Otherwise, if a number exists with those properties, then the component requests a memory update action that replaces the old number with its incremented value. As pointed out when discussing working memory, these requests must receive the focus of attention to be processed in ARCADIA’s cycle. Attentional Strategy An attentional strategy for this task requires the system to preferentially attend to an object, detect color changes, and increment a counter accordingly. Because memory operations have type “action,” the additional components combined with the attentional strategy in figure 3 already enable Figure 5: ARCADIA visualizations while (left) untasked and (right) tasked with counting changes. The top left window in each image shows objects stored in vSTM. The bottom left window shows an iconic representation of ARCADIA’s view where objects are picked out. Red boxes indicate where working memory representations were last updated, the pink box indicates the current visual fovea, green boxes are candidate fixations. The window to the right is the bottom-up saliency map. In both instances, the star is more salient than the circle. the system to detect changes and increment a counter. However, if a salient distractor impinges on ARCADIA’s visual field, will be drawn away from the object that it is tracking, potentially missing changes. To indicate the importance of the task, we make one minor modification to the previous strategy. Recall that the change detection strategy involved, at level 5, a task-general preference for a candidate fixation. When the strategy uses this preference to select the next focus of attention, the system chooses a candidate fixation randomly from those that are available. In that case, ARCADIA may be drawn away from a task-relevant object to foveate on a salient distractor. To prevent this behavior, we modify the attentional strategy to prefer fixating on objects represented in vSTM over those regions that are suggested by bottom-up feature computations. To restate, we use the attentional strategy to encode that it is more important to continue looking at the task-relevant object (i.e., the moving circle) than to look toward anything else (i.e., the red star). Resulting Behavior As illustrated in figure 5, ARCADIA behaves as predicted. The image on the left, which was produced using the attentional strategy in figure 3, shows ARCADIA’s focus squarely on the distractor and two objects in vSTM. In contrast, the image on the right, which used the modified attentional strategy, shows that ARCADIA visually attends only to the circle throughout the scenario. Importantly, the associated saliency maps (where brighter pixels represent greater saliency) indicate that the red star coincides with the most salient region in both cases. Notice in both cases that the distractor is processed by low-level visual components, but never attains an object representation due explicitly to a lack of attention. Future Directions and Concluding Remarks These results are only the first steps in building a general, taskable cognitive-system that perceives, deliberates about, and acts within the world. To this end we are implementing an auditory saliency map (Kayser et al. 2005), taking the first step toward interpreting audio signals within ARCADIA with an eye toward multi-sensory integration. We also intend to develop a theory of long-term memory and attentive recollection where memories are multi-representational in nature, containing perceptual properties (Morsella et al. 2009). Further, recollection will be modulated by internally directed attention (De Brigard 2012). At the higher-level end of cognitive activity, we will be implementing models of deliberative reasoning informed by mental model theory (Khemlani, Barbey, and Johnson-Laird 2014). Readers of this paper may find themselves mystified about why anyone would build such a capacity-limited system and then portray the expression of those limitations as markers of success. We address the first part of the question by making the uncontroversial claim that regardless of the available computational resources, there will always be too much data to process everything in full. This is true whether we are talking about autonomous systems operating within the world or cognitive aids that assist people in making sense from mounds of data. To handle this problem, people design systems with resource limitations in mind, hard coding their expectations about what must or must not be processed. 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