• Chen & Scholl
• Firestone & Scholl
• Uddenberg & Scholl
• van Buren, Uddenberg & Scholl
• Ward & Scholl

The perception of shape, it has been argued, also often entails the perception of time. A cookie with a bite taken out of it, for example, is seen as a whole cookie that was subsequently bitten. Similarly, a twisted towel is represented as an untwisted towel that was subsequently twisted. It has never been clear, however, whether such observations truly reflect visual processing alone. To explore this, we tested whether the perception of history in static shapes is powerful enough to influence the perception of other visual features. Observers were told that they would see short movies of a shape (e.g. a square) changing from its complete form into a truncated form, with a "piece" of it missing, and that this change could occur in two ways: (1) all at once, in a single flash; or (2) gradually, with the missing piece quickly "growing" into the shape (as when you poke your finger into a lump of clay). Our primary manipulation involved the contours of the missing piece itself. On some trials, these contours implied a causal history: the static result looked as if another shape had at one time 'intruded' on the original shape. On other trials, these contours implied no such past gradual transformation. When presented as an actual change (from the full shape to the truncated shape), this variable influenced whether observers actually perceived motion. In particular, when the contours of the missing piece suggested a type of historical 'intrusion', observers actually saw that intrusion occur: it appeared as if the change actually occurred gradually, in a type of transformational apparent motion. (Catch trials with real gradual motion ruled out the possibility of a response bias.) Thus the perception of causal history in shapes is powerful enough to induce illusory motion percepts.

Some figures are irresistibly seen as complete objects. Others are represented as mere collections of line segments. How does the visual system represent figures in between these extremes -- say, when part of a figure strongly suggests a complete object, while another part strongly suggests an open contour? More generally, how do we represent figures that are ambiguous or underdetermined with regard to 'shapehood'? We explored these questions using the "tap-the-shape" task, which reveals the so-called "skeletons" (internal symmetry-defined geometric structures) that underlie human shape representation: when a subject is shown a shape on a touch-sensitive tablet computer and is instructed simply to tap the shape once anywhere they please, the aggregated taps from hundreds of observers collectively form that shape's skeleton (Firestone & Scholl, 2014, Psychological Science). Here we exploit this striking phenomenon to ask a more fundamental question: what is a shape in the first place? Across several experiments, we showed thousands of observers ambiguous or incomplete shapes, and asked them to tap "inside" those figures (with one tap and one shape per subject). Remarkably, ambiguous figures -- e.g. a rectangle with one missing edge -- were represented in a hybrid manner: touches near the 'inside' edge formed clear skeletal branches, while touches near the open edge devolved into noise. We also tested 'open' figures that were ambiguous between multiple complete interpretations. For example, a trapezoid missing its top edge -- which can be seen as either a trapezoid or a triangle -- was tapped as though it had both the shape skeleton of a triangle and the shape skeleton of a trapezoid. We discuss the significance of these apparent hybrid representations for theories of shape, and for use of the "tap-the-shape" method to study previously stubborn questions about visual representations.

Great strides have been made in recent years in understanding how we perceive faces in terms of underlying "face spaces". Our work is focused on the relatively unexplored notion of default regions of these spaces, toward which our face representations may be attracted. Picture a person standing before you, asking for directions. Now consider: what did that person look like? And where did that information come from? Here we used a novel instantiation of the method of serial reproduction to explore the effective 'default settings' in face space. As a first case study, we explored the perception of race. A single face was briefly presented to each observer, with its race selected from a smooth continuum between White and Black (with all faces matched for mean luminance). The observer then simply reproduced that face, by using a slider to morph a test face along this continuum. Their response was then used as the face initially presented to the next observer, and so on down the line in each reproduction chain. This method has been shown (albeit in very different contexts) to reveal the contents of people's default assumptions about the world. In our experiments, White observers' reproduction chains consistently and steadily converged onto faces that were significantly Whiter than both the original face and the continuum's midpoint. Indeed, even chains beginning near the Black end of the continuum inevitably ended up well inside the White region. These results highlight a default region of face space for White observers, which biases downstream perception and memory. In further experiments, we report extensions both to other cultures (e.g. exploring White and Indian observers' face-space defaults in race continua from White to South Asian faces) and to other types of features (in particular, continua that vary faces' age, gender, and perceived animacy).

Visual processing recovers not only simple features such as color and shape, but also seemingly higher-level properties such as animacy and intentionality. Indeed, even abstract geometric shapes are readily perceived as intentional agents when they move in certain ways, and such percepts can dramatically influence behavior. In the wolfpack effect, for example, participants maneuver a disc around a display that contains a number of randomly-moving dart shapes, which they must avoid. When the darts collectively point toward the user-controlled disc, however, participants (falsely) perceive that the darts are chasing them, and they perform substantially worse than when the darts are always oriented perpendicular to the disc (a control condition that perfectly equates the degree of correlated motion). However, the nature of such effects, despite their power, remains unclear. Are they reflexive, automatic features of visual processing? Or might they instead arise only as contingent strategies in tasks where participants must interact with (and thus focus on the features of) such objects? We explored these questions in an especially direct way -- by simply embedding such displays into the background of a completely independent 'foraging' task. Participants now moved their disc to collect small dots (which appeared sequentially in random locations) as quickly as possible. The darts were task-irrelevant, and participants were encouraged to simply ignore them. Nevertheless, foraging was significantly slowed when the randomly-moving darts all pointed at the participant-controlled disc -- compared to control conditions when the darts either (1) were always oriented perpendicular to the participant-controlled disc, or (2) always pointed at a separate (and also task-irrelevant) moving shape. The perception of animacy may thus influence downstream visuomotor behavior in a reflexive, automatic manner, such that participants cannot override the influences of seemingly animate shapes while attempting to completely ignore them.

Perhaps the most striking phenomenon of visual awareness is inattentional blindness (IB), in which a surprisingly salient event right in front of you may go completely unseen when unattended. Does IB reflect a failure of online perception, or only of subsequent encoding into memory -- a form of "inattentional amnesia" (e.g. Wolfe, 1999)? Previous work has been unable to answer this question, due to a seemingly intractable dilemma: ruling out memory requires immediate perceptual reports, but soliciting such reports fuels an expectation that eliminates IB. Here we introduce a way to escape this dilemma, reporting two experiments that evoke repeated IB in the same observers, in the same session, and even when unexpected events must be immediately reported, mid-event. We employed a sustained IB task: after several trials of a demanding primary tracking task, an Unexpected Event (UE) occurred: a new object (with a novel shape, color, and motion direction compared to everything else in the display) appeared, after which observers were asked (in various ways) whether they had noticed it. Subsequently, observers had to immediately press a key any time (throughout the rest of the experiment) they saw something different or unexpected. Observers made use of such keypresses when the very same UE was later repeated, but when an equivalent UE with entirely new features (now differing in color, shape, and motion direction from all of the other objects and from the previous UE) subsequently appeared, observers failed to report it -- even mid-event, during the 5 seconds that it traversed the display. Thus, observers fail to see salient events not only when they have no expectation, but also when they have the wrong expectations. These experiments demonstrate that IB is aptly named: it reflects a genuine deficit in moment-by-moment conscious perception, rather than a form of inattentional amnesia.