(Treisman 2003) allowing us to experience a world of co- herent, integrated objects instead of disembodied or wrong- ly-combined shapes, colors, motions, and sizes (Treisman 1998). !e combined system of visual object binding and short-term memory is called “visual binding working mem- ory”, or simply “binding memory.” It is what allows people to experience, for example, a ball "ying through the air as a single moving object, instead of as snapshots of identical balls tracing a path through space. Binding memory is an indispensable part of biological motion detection. Basic evidence for the existence of binding memory Recent developments in binding memory research, elu- cidating its properties and limitations, promise to expand scienti#c understanding of biological motion detection. Several experiments have con#rmed the premise of binding memory: that features of objects are #rst perceived sepa- rately before being bound together into a uni#ed object. For example, in one experiment, subjects were shown col- lections of squares with varying orientations that were laid out in a grid, and they were asked to recall features of the squares at particular grid locations after a short delay (Bays et al., 2011). Interestingly, subjects often failed to recall which features went with which object, rather than forget- ting the object altogether. !is suggests that people perceive the separate features of an object individually, rather than as a single uni#ed object, and have separate categories for di$erent features (e.g. color, shape, and orientation). In a similar experiment, researchers started from a base- line of three objects with six di$erent features (Wheeler et al., 2002). When they doubled the number of objects, there was no appreciable change in recall performance, but halv- ing the number of features resulted in a signi#cant increase in performance recall. !is suggests that perception can be limited by the number of features, but not by the number of objects. !ese results were further supported by a simi- lar study, where subjects were brie"y shown objects on a screen, followed by a blank interval, and were then asked to choose the object they had seen from an array of similar types of objects (Alvarez et al., 2004). !eir capacity for re- membering these objects varied widely, with a greater num- ber of features to be recalled correlating with a decrease in performance. Since the increase in the number of features but not the number of objects led to a decrease in memo- ry performance, it is likely that that features of objects are held separately in short term memory and then subsequent- ly integrated. !is is a limit of human binding memory: subjects’ performance in object-recall tasks depend on the number features the objects have. E!ects of old age and disease on binding memory Recent studies have also explored the e$ects of old age and diseases such as autism spectrum disorders (ASD) and schizophrenia on binding memory. For example, functional magnetic resonance imaging (fMRI) measurements of brain activity were taken in ASD patients as they performed a biological motion detection task (Herrington et al., 2007). !e ASD subjects showed less activity in the fusiform gy- rus as compared to control subjects, an area previously im- plicated in the processing of visual feature binding. !ese results #t with those of another study in which autistic and normal children were asked to perform two tasks: one in- volving the detection of abstract shapes in a still image, and one involving the detection of biological motion (Blake et al., 2003). Performance for both groups was similar on the #rst task, but the autistic children performed far worse on the task with the simulated biological motion. !is sup- ports the claim that autistic individuals generally have more trouble binding orientation and position information to- gether through time, and thus have a harder time detecting biological motion. Studies with another disease, schizophrenia, have also highlighted the critical importance of binding memory and biological motion detection by showing what happens when there is a binding memory de#cit. In a study with schizophrenic patients, visual working memory was tested for two features of drawings of familiar items: their location in a grid, and the identity of the item (Burglena et al., 2003). !e test was done under two sets of circumstances: in the #rst, subjects were asked to simply recall the features independently. Speci#cally, they had to say where on the grid an ob- ject had been displayed (regardless of which object), or what object had appeared (regardless of where). In the second set of circumstances, subjects were asked to recall an object and its location (a test of binding memory). Although schizophrenic patients generally have impaired working memory, this experiment’s re- sults showed that they had disproportionately poor perfor- mance in binding memory. Yet another study explored the e$ects of age on binding (Kessels et al., 2007). Young adults (mean age of 25) and older adults (mean age of 66) were asked to view a series of familiar objects displayed on a grid. !ey were then asked to recall either just the objects, just the grid locations that were occupied, or both the object and the grid location in which it was displayed. Even after taking into account the fact that memory generally declines with age, the older adults had disproportionately poor performance on the #- nal task. !is suggests that binding memory performance declines markedly with age, and to an even greater degree than other kinds of memory. !e fact that autism and schizophrenia – broad and se- vere cognitive disturbances – correlate with binding mem- ory problems underscores the relevance of this ability to normal human cognition (Herrington et al., 2007, Blake et al., 2003, Burglen et al., 2003). :H�UHYLHZ�WKH�OLWHUDWXUH�WR�GDWH�RQ�ELRORJLFDO�PRWLRQ�GHWHFWLRQ�DQG�LWV�LPSRUWDQW�SUHUHTXLVLWH��KXPDQ�ELQGLQJ�PHPRU\��%LQGLQJ� memory is the system for combining features like shape, color and size into coherent visual objects, and tracking these objects through time in short-term memory. This in turn makes possible biological motion detection, which is crucial to a wide range of human social ac- tivity. Recent experiments have shown that binding memory is available from birth, declines with old age, and is improved by emotional arousal. Furthermore, binding memory has been shown to be disturbed in neurological disorders such as autism and schizophrenia. These results promise to contribute to a greater understanding of biological motion detection in the future. Columbia Undergraduate Science Journal Open-Access Publication | http://cusj.columbia.edu 23 cusjVolume 6Spring 2012 Columbia Undergraduate Sci J http://cusj.columbia.edu + 8 0 $ 1 �% ,2 /2 * < cusjcolumbia undergraduate science journal Review Articles 24cusj Volume 6Spring 2012 Columbia Undergraduate Sci J http://cusj.columbia.edu + 8 0 $ 1 �% ,2 /2 * < Biological motion detection Humans have a specialized system called biological motion detection that responds specially to the move- ments of living creatures. More speci#cally, biological motion detection is the cognitive process whereby the perception of motion patterns characteristic of living organisms evoke a compelling impression that a living thing is being observed (Johansson 1973). !is distinct neurological process is important for developing an un- derstanding of the minds of others, and for function- ing socially in general; human understanding of what is and is not a living thing is based on cues including motion – such as walking, speaking, or yawning – and social skills are predicated on the ability to readily dis- criminate between living and non-living things (Blake et al., 2007). Biological motion detection – which exists in a wide va- riety of animals including chickens (Simion et al., 2008) and macaques (Oram et al.,1994) – is functional in hu- mans almost from birth (Simion et al., 2008). When two- day-old infants were shown various rudimentary anima- tions consisting of black dots moving around on a white background, they spent more time looking at the patterns that resembled an upright, walking animal than any of the others. Because the animations used were so simple – com- prised of just 13 dots and 23 looping frames of video – they are unintelligible jumbles when motionless. !e fact that the infants could discriminate di$erent moving patterns of objects from each other at birth indicates that they must al- ready have some sort of functioning binding memory. !is result seems to #t with the fact that binding memory does not require the hippocampus, a brain area widely impli- cated in memory but not functional at birth. In trials with a patient with severe hippocampal damage, binding memory (as measured by color- and shape-recognition tasks de- scribed below) for the patient was no di$erent than that of control subjects (Baddeley et al., 2010). !e fact that newborns can detect biological motion from the simplest patterns (Simion et al., 2008) with an ability that does not depend, like so many other memo- ry processes, on the hippocampus suggests that this is an important component of human cognition with highly- specialized neural correlates. In typical humans, biological motion detection has been localized to a small area in the superior-temporal sulcus (STS) (Grossman et al., 2000). !is brain region was found to be sensitive to motion typi- cal of animate creatures, and showed greater activation even when the body plan was reduced to abstract, simpli#ed points of light moving in a pattern reminiscent of animal motion. Despite the unitary, integrated nature of the perceptual experience of biological motion detection – and the ease with which the brain typically performs this task – this ability only arises through the coordinated e$ort of sev- eral complex systems in di$erent parts of the brain. As the points-of-light experiment demonstrated, the low-level components of biological motion are simply visual stimuli with certain shapes, orientations, motions and colors as- sociated with them. To detect biological motion, the brain must appropriately process these components in concert. A closer look at how this processing works indicates that the brain perceives visual features (e.g. color, shape, and orientation) individually, and then uses short-term working memory to “bind” them together into a unitary experience, Low-Level Visual Processing Allows Humans to React to Animate Objects: Binding Memory as a Key Subsystem of Biological Motion Detection Andrew Hamilton* Copyright: © 2012 The Trustees of Columbia University, Columbia University Libraries, some rights reserved, Hamilton. Received 12/31/2012. Accepted 2/6/2012. Published 4/1/2012 *To whom correspondence should be addressed: ah2926@columbia.edu Abstract E!ects of attention and emotional arousal in binding memory !e e"ects of attention and emotional arousal in the function of binding memory have been explored experimen- tally as well. In one study, subjects were shown shapes with distinctive colors and orientations on a computer screen (Johnson et al., 2008). !ey were then asked to state either which features had been simply present (to test memory but not binding), or which features had gone with which shape (to test binding). Performance was evaluated both in the presence and absence of distracting stimuli. Interestingly, the presence of a distraction impaired performance equally for individual feature recall as well as bound object recall. In other words, the fact that the subjects’ being distracted did not speci#cally impede their feature binding any more than it did the processing of the features alone indicates that one need not pay attention to an object to properly process it together with all of its features. In another study, subjects were shown words of varying colors and levels of emotional signi#cance (e.g. “slaugh- ter” or “emergency” for highly-emotional words, and “taxi” or “dormitory” for neutral words) (Doerksen et al., 2001). !ey were then asked to recall either one separate feature of the object (e.g. the word), another feature (e.g. the color), or the bound object (e.g. the word and the color it was displayed in). Unsurpris- ingly, subjects exhibited an enhanced recall for highly emotional words. However, a high emotional valence also enhanced recall for the associated color, suggest- ing a binding e"ect. In other words, emotional arousal enhances not only memory, but binding e$ciency as well. !ese are surprising strengths: binding memory can function even when people are not paying atten- tion and can actually be improved by emotional arousal. Future directions Biological motion detection is so important that it be- comes functional almost immediately out of the womb and underpins people’s basic ability to interact with each other (Simion et al., 2008). More research into binding memory is needed to gain a greater understanding of biological mo- tion detection and the corresponding elements of high-level social cognition. Not enough is known about what other lower-level systems aside from feature binding are indispen- sible to biological motion detection. Further research is also needed to determine the extent to which feature binding de#cits in pathological cases con- tribute to problems with biological motion detection, in order to learn more precisely just how much it depends on binding. !is might be accomplished by combining some of the experimental paradigms above to explore the e"ects of conditions like emotional arousal on binding and mo- tion detection in subjects with neurological disorders. Furthermore, more work is required to understand the neural correlates of binding memory in cases of these neu- rological diseases, particularly those with salient social im- plications, such as Alzheimer’s, ASD, and schizophrenia. Advances in this area promise to not only enrich the un- derstanding of how biological motion detection works in humans, but of the pathologies themselves. Alvarez GA, Cavanagh P. “!e Capacity of Visual Short-Term Memory is Set Both by Visual Information Load and by Number of Objects.” Psychol Sci 15:2 (2004) 106-111 Baddeley A, Allen R, Vargha-Kadem F. “Is the hippocampus necessary for visual and verbal binding in working memory?” Neuropsychologia 48 (2010) 1089–1095 Bays M, Wu E, Husain M. “Storage and binding of object features in visual working memory.” Neuropsychologia 49(6), (2011), 1622-1631 Blake R, Shi"rar M. “Perception of human motion.” Annu. Rev. Psy- chol.58 (2007) 47–73 Blake R, Turner L, Smoski MJ, Pozdol SL, Stone WL. “Visual recogni- tion of biological motion is impaired in children with autism.” Psychol Sci. (2003), 14(2):151-7. Burglena F, Marczewski P, Mitchell K, van der Linden M, Johnson M, Danion J, Salame P. “Impaired performance in a working memory bind- ing task in patients with schizophrenia.” Psychiatry Research 125 (2004) 247–255 Doerksen S, Shimura A. “Source Memory Enhancement for Emotional Words.”Emotion (2001), (I)1 5 – 11 Grossman E, Donnelly M, Price R, Pickens D, Morgan V, Neighbor G, Blake R. “Brain Areas Involved in Perception of Biological Motion.” J. Cogn. Neurosci. 12:5 (2000), 711–720 Herrington J, Baron-Cohen S, Wheelwright S, Singh K, Bullmore E, Brammer M, Williams S. “!e role of MT+/V5 during biological motion perception in Asperger Syndrome: An fMRI study.” Research in Autism Spectrum Disorders 1 (2007) 14–27 Johansson G. “Visual perception of biological motion and a model for its Analysis”, Perception Psychophys. 14(2), (1973), 201–211. Johnson J, Hollingworth A, Luck S. “Role of Attention in the Mainte- nance of Feature Bindings in Visual Short-Term Memory.” J Exp Psychol Hum Percept Perform. (2008), 34(1): 41–55. Columbia Undergraduate Science Journal Open-Access Publication | http://cusj.columbia.edu 25 cusjVolume 6Spring 2012 Columbia Undergraduate Sci J http://cusj.columbia.edu + 8 0 $ 1 �% ,2 /2 * < Kessels R. C., Hobbel, D., & Postma, A. “Aging, Context Memory And Binding: A Comparison Of ‘What, Where And When’ In Young & Older Adults”. Intl J. Neurosci 117:6 (2007), 795-810. Oram MW, Perrett DI. “Responses of anterior superior temporal poly- sensory (STPa) neurons to ‘biological motion’ stimuli”. J. Cogn. Neurosci. 6, (1994) 99–116. Saiki J, Miyatsuji H. “Feature binding in visual working memory evalu- ated by type identi#cation paradigm.” Cognition 102 (2007) 49–83. Simion F, Regolin L, Bulf H. “A predisposition for biological motion in the newborn baby.” Proc Natl Acad Sci U S A. (2008), 105(2):809-13. Treisman A. “Consciousness and perceptual binding.” In A. Cleeremans, ed., !e Unity of Consciousness: Binding, Integration, Dissociation.Oxford University Press, 2003. Treisman A. “Feature binding, attention and object perception.” Phil. Trans. R. Soc. Lond. B (1998) 353, 1295-1306. Wheeler M, Treisman A. “Binding in Short-Term Visual Memory.” Jour- nal of Experimental Psychology (2002), 131(1), 48–64 cusjcolumbia undergraduate science journal Review Articles 26cusj Volume 6Spring 2012 Columbia Undergraduate Sci J http://cusj.columbia.edu + 8 0 $ 1 �% ,2 /2 * < References