Neural evidence for competition-mediated suppression in the perception of a single object

The hidden arrow in the FedEx logo: Do we really unconsciously "see" it?

The FedEx logo makes clever use of figure-ground ambiguity to create an "invisible" arrow in the background space between "E" and "x". Most designers believe the hidden arrow can convey an unconscious impression of speed and precision about the FedEx brand, which may influence subsequent behavior. To test this assumption, we designed similar images with hidden arrows to serve as endogenous (but camouflaged) directional cues in a Posner's orienting task, where a cueing effect would suggest subliminal processing of the hidden arrow. Overall, we observed no cue congruency effect, unless the arrow is explicitly highlighted (Experiment 4). However, there was a general effect of prior knowledge: when people were under pressure to suppress background information, those who knew about the arrow could do so faster in all congruence conditions (i.e., neutral, congruent, incongruent), although they fail to report seeing the arrow during the experiment. This was true in participants from North America who had heard of the FedEx arrow before (Experiment 1 & 3), and also in our Taiwanese sample who were just informed of such design (Experiment 2). These results can be well explained by the Biased Competition Model in figure-ground research, and together suggest: (1) people do not unconsciously perceive the FedEx arrow, at least not enough to exhibit a cueing effect in attention, but (2) knowing about the arrow can fundamentally change the way we visually process these negative-space logos in the future, making people react faster to images with negative space regardless of the hidden content.

BOLD activation on the groundside of figures: More suppression of grounds that competed more for figural status

A fundamental aspect of object detection is assigning a border to one (figure) side but not the other (ground) side. Figures are shaped; grounds appear shapeless near the figure border. Accumulating evidence supports the view that the mechanism of figure assignment is inhibitory competition with the figure perceived on the winning side. Suppression has been observed on the groundside of figure borders. One prediction is that more suppression will be observed when the groundside competes more for figural status. We tested this prediction by assessing BOLD activation on the groundside of two types of stimuli with articulated borders: AE_nov and AE_fam stimuli. In both stimulus types, multiple image-based priors (symmetry, closure, small area, enclosure by a larger region) favored the inside as the figure. In AE_fam but not AE_nov stimuli, the figural prior of familiar configuration present on the outside competes for figural status. Observers perceived the insides of both types of stimuli as novel figures and the outsides as shapeless grounds. Previously, we observed lower BOLD activation in early visual areas representing the grounds of AE_fam than AE_nov stimuli, although unexpectedly, activation was above baseline. With articulated borders, it can be difficult to exclude figure activation from ground ROIs. Here, our ground ROIs better excluded figure activation; we also added straight-edge (SE) control stimuli and increased the sample size. In early visual areas representing the grounds, we observed lower BOLD activation on the groundside of AE_fam than AE_nov stimuli and below-baseline BOLD activation on the groundside of SE and AE_fam stimuli. These results, indicating that greater suppression is applied to groundsides that competed more for figural status but lost the competition, support a Bayesian model of figure assignment in which proto-objects activated at both low and high levels where image features and familiar configurations are represented, respectively, compete for figural status.

Normative data for an expanded set of stimuli for testing high-level influences on object perception: OMEFA-II

We present normative data for an expanded set of stimuli designed to investigate past experience effects on object detection. The stimuli are vertically-elongated “bipartite” displays comprising two equal-area regions meeting at an articulated central border. When the central border is assigned to one side, a shaped figure (i.e., an object) is detected on that side. Participants viewing brief masked exposures typically detect figures more often on the critical side of Intact displays where a common (“familiar”) object is depicted than on a matched critical side of Part-Rearranged (PR) displays comprising the same parts arranged in novel configurations. This pattern of results showed that past experience in the form of familiar configuration rather than familiar parts is a prior for figure assignment. Spurred by research implicating a network involving the perirhinal cortex of the medial temporal lobe in these familiar configuration effects, we enlarged the stimulus set from 24 to 48 base stimuli to increase its usefulness for behavioral, neuropsychological, and neuroimaging experiments. We measured the percentage of participants who agreed on a single interpretation for each side of Intact, Upright PR, and Inverted PR displays (144 displays; 288 sides) under long exposure conditions. High inter-subject agreement is taken to operationally define a familiar configuration. This new stimulus set is well-suited to investigate questions concerning how parts and wholes are integrated and how high- and low-level brain areas interact in object detection. This set also allows tests of predictions regarding cross-border competition in figure assignment and assessments of individual differences. The displays, their image statistics, and normative data are available online (https://osf.io/j9kz2/).

Image Segmentation Based on Relative Motion and Relative Disparity Cues in Topographically Organized Areas of Human Visual Cortex

The borders between objects and their backgrounds create discontinuities in image feature maps that can be used to recover object shape. Here we used functional magnetic resonance imaging to identify cortical areas that encode two of the most important image segmentation cues: relative motion and relative disparity. Relative motion and disparity cues were isolated by defining a central 2-degree disk using random-dot kinematograms and stereograms, respectively. For motion, the disk elicited retinotopically organized activations starting in V1 and extending through V2 and V3. In the surrounding region, we observed phase-inverted activations indicative of suppression, extending out to at least 6 degrees of retinal eccentricity. For disparity, disk activations were only found in V3, while suppression was observed in all early visual areas. Outside of early visual cortex, several areas were sensitive to both types of cues, most notably LO1, LO2 and V3B, making them additional candidate areas for motion- and disparity-cue combination. Adding an orthogonal task at fixation did not diminish these effects, and in fact led to small but measurable disk activations in V1 and V2 for disparity. The overall pattern of extra-striate activations is consistent with recent three-stream models of cortical organization.

Semantic category priming from the groundside of objects shown in nontarget locations and at unpredictable times

Previous research demonstrated that familiar objects that are suggested, but not consciously perceived, on the groundside of the contours of a figure activate their semantic category during perceptual organization, at least when the figure appears at fixation at an expected time. Here, we investigate whether evidence for such semantic activation extends to stimuli presented at unpredictable times in peripheral locations. Participants categorized words shown centrally as denoting natural or artificial objects (Experiments 1 and 2a) or positive or negative concepts (Experiment 2b). Prior to the word, two distractor silhouettes appeared above and below fixation; both depicted novel figures. On experimental trials, portions of well-known (familiar) objects were suggested on the groundside of the borders of one (Experiment 1) or both (Experiment 2a and 2b) silhouettes. In Experiment 1, reaction times were slower when targets words were preceded by experimental distractor silhouettes regardless of whether the object suggested on the groundside of their borders was in the same or a different category as the object denoted by the word. Overall slowing may have occurred because (a) semantic category access by objects suggested on the groundside of experimental distractor silhouettes was sufficient to require filtering but not category-specific priming, (b) more competition for object status slowed processing of experimental compared to control silhouettes, or (c) featural differences increased the difficulty of processing the experimental versus the control silhouettes. The use of two identical experimental silhouettes in Experiment 2a allowed a semantic category priming effect to emerge, showing that the categories of objects suggested on the groundside of silhouette borders can be activated at unpredictable times in nontarget locations and in more than one location of the visual field. Experiment 2a suggested that (a) better explains the results of Experiment 1 than (b and c). Experiment 2b further ruled out explanations (b and c) as reasons for the Experiment 1 results by showing that the same pattern is not obtained when the semantic category of the objects suggested on the groundside of the experimental silhouettes borders is not task-relevant and does not require filtering. Thus, spatial prime-target congruence and temporal certainty are not necessary for priming by objects suggested on the groundside of figures. Implications for our understanding of the complex processes involved in perceptual organization are considered.

Age-Related Changes in Perirhinal Cortex Sensitivity to Configuration and Part Familiarity and Connectivity to Visual Cortex

The perirhinal cortex (PRC) is a medial temporal lobe (MTL) structure known to be involved in assessing whether an object is familiar (i.e., meaningful) or novel. Recent evidence shows that the PRC is sensitive to the familiarity of both whole object configurations and their parts, and suggests the PRC may modulate part familiarity responses in V2. Here, using functional magnetic resonance imaging (fMRI), we investigated age-related decline in the PRC's sensitivity to part/configuration familiarity and assessed its functional connectivity to visual cortex in young and older adults. Participants categorized peripherally presented silhouettes as familiar ("real-world") or novel. Part/configuration familiarity was manipulated via three silhouette configurations: Familiar (parts/configurations familiar), Control Novel (parts/configurations novel), and Part-Rearranged Novel (parts familiar, configurations novel). "Real-world" judgments were less accurate than "novel" judgments, although accuracy did not differ between age groups. The fMRI data revealed differential neural activity, however: In young adults, a linear pattern of activation was observed in left hemisphere (LH) PRC, with Familiar > Control Novel > Part-Rearranged Novel. Older adults did not show this pattern, indicating age-related decline in the PRC's sensitivity to part/configuration familiarity. A functional connectivity analysis revealed a significant coupling between the PRC and V2 in the LH in young adults only. Older adults showed a linear pattern of activation in the temporopolar cortex (TPC), but no evidence of TPC-V2 connectivity. This is the first study to demonstrate age-related decline in the PRC's representations of part/configuration familiarity and its covariance with visual cortex.

Increased alpha band activity indexes inhibitory competition across a border during figure assignment

Figure-ground assignment is thought to entail inhibitory competition between potential objects on opposite sides of a shared border; the winner is perceived as the figure, and the loser as the shapeless ground. Computational models and response time measures support this understanding but to date no online measure of inhibitory competition during figure-ground assignment has been reported. The current study assays electroencephalogram (EEG) alpha power as a measure of inhibitory competition during figure-ground assignment. Activity in the EEG alpha band has been linked to functional inhibition in the brain, and it has been proposed that increased alpha power reflects increased inhibition. In 2 experiments participants viewed silhouettes designed so that the insides would be perceived as figures. Real-world silhouettes depicted namable objects. Novel silhouettes depicted novel objects on the insides of their borders, but varied in the amount of hypothesized cross-border competition for figural status: In "Low-Competition" silhouettes, the borders suggested novel objects on the outside as well as on the inside. In "High-Competition" silhouettes the borders suggested portions of real-world objects on the outside; these compete with the figural properties favoring the inside as figure. Participants accurately categorized both types of novel silhouettes as "novel" objects and were unaware of the real world objects suggested on the outside of the High-Competition silhouettes. In both experiments, we observed more alpha power while participants viewed High- rather than Low-Competition novel silhouettes. These are the first results to show via an online index of neural activity that figure assignment entails inhibitory competition.