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Do individuals prefer stimuli that are ordered or disordered, simple or complex, or that strike the right balance of order and complexity? Earlier research mainly focused on the separate influence of order and complexity on aesthetic appreciation. When order and complexity were studied in combination, stimulus manipulations were often not parametrically controlled, only rather specific types of order (i.e., balance or symmetry) were usually studied, and/or the multidimensionality of order and complexity was largely ignored. Progress has also been limited by the lack of an easy way to create reproducible and expandible stimulus sets, including both order and complexity manipulations. The Order & Complexity Toolbox for Aesthetics (OCTA), a Python toolbox that is also available as a point-and-click Shiny application, aims to fill this gap. OCTA provides researchers with a free and easy way to create multi-element displays varying qualitatively (i.e., different types) and quantitatively (i.e., different levels) in order and complexity, based on regularity and variety along multiple element features (e.g., shape, size, color, orientation). The standard vector-based output is ideal for experiments on the web and the creation of dynamic interfaces and stimuli. OCTA will not only facilitate reproducible stimulus construction and experimental design in research on order, complexity, and aesthetics. In addition, OCTA can be a very useful tool in any type of research using visual stimuli, or even to create digital art. To illustrate OCTA’s potential, we propose several possible applications and diverse questions that can be addressed using OCTA.

Previous research on perceptual grouping has focussed on discovering and understanding grouping principles and their interactions on both a group and an individual level. However, the studied set of grouping principles does not consider the complexity of interactions between the local and global level. In this study, dot lattices were adjusted to have various oriented shapes as elements. In addition to proximity between the elements, the use of triangles as elements provided a direct (i.e., alignment of the shape’s side and the global orientation promoting good continuation) as well as an indirect grouping cue (i.e., perceived pointing in local triangles as a result of its global reference frame) promoting global groupings. We replicated the well-studied proximity effect. In addition, the introduction of shapes as elements resulted in a dampening of the proximity effect, regardless of the nature of the shape. The grouping effect of triangles, however, was dependent on the grid characteristics and differed between individuals. In a grid with small elements, most participants adhered to grouping by pointing . When the size of the elements was increased, there was a shift towards grouping by base-alignment . In both grid types, a relatively large group of participants did not exhibit consistent grouping by alignment nor pointing . These results confirm that oriented shapes can function as grouping cues in both a direct (i.e., alignment ) and an indirect (i.e., pointing ) manner. Moreover, they emphasize the importance of studying individual differences in perceptual grouping.

Perceptual grouping of line segments into object contours has been thought to be mediated, in part, by long-range horizontal connectivity intrinsic to the primary visual cortex (V1), with a contribution by top-down feedback projections. To dissect the contributions of intraareal and interareal connections during contour integration, we applied conditional Granger causality analysis to assess directional influences among neural signals simultaneously recorded from visual cortical areas V1 and V4 of monkeys performing a contour detection task. Our results showed that discounting the influences from V4 markedly reduced V1 lateral interactions, indicating dependence on feedback signals of the effective connectivity within V1. On the other hand, the feedback influences were reciprocally dependent on V1 lateral interactions because the modulation strengths from V4 to V1 were greatly reduced after discounting the influences from other V1 neurons. Our findings suggest that feedback and lateral connections closely interact to mediate image grouping and segmentation.

Grouping sets of elements into smaller, equal-sized, subsets constitutes a perceptual strategy employed by humans and other animals to enhance cognitive performance. Here, we show that day-old chicks can solve extremely complex numerical discriminations (Exp.1), and that their performance can be enhanced by the presence of symmetrical/asymmetrical colour grouping (Exp.2 versus Exp.3). Newborn chicks were habituated for 1 h to even numerosities (sets of elements presented on a screen) and then tested for their spontaneous choice among what for humans would be considered a prime and a non-prime odd numerosity. Chicks discriminated and preferred the prime over the composite set of elements irrespective of its relative magnitude (i.e. 7 versus 9 and 11 versus 9). We discuss this result in terms of novelty preference. By employing a more complex contrast (i.e. 13 versus 15), we investigated the limits of such a mechanism and showed that induced grouping positively affects chicks' performance. Our results suggest the existence of a spontaneous mechanism that enables chicks to create symmetrical (i.e. same-sized) subgroups of sets of elements. Chicks preferentially inspected numerosities for which same-sized grouping is never possible (i.e. the prime numerosity) rather than numerosities allowing for symmetrical grouping (i.e. composite).

It has previously been shown that grouping by proximity is well described by a linear function relating the perceived orientation of a dot lattice to the ratio of the distances between the dots in the different orientations. Similarly, luminance influences how observers perceptually group stimuli. Using the dot lattice paradigm, it has been shown that proximity and luminance similarity interact additively, which means that their effects can be summed to predict an observers’ percept. In this study, we revisit the additive interplay between proximity and luminance similarity and we ask whether this pattern might be the result of inappropriately averaging different types of observers or the imbalance between the strength of proximity grouping and luminance similarity grouping. To address these questions, we first ran a replication of the original study reporting the additive interplay between proximity and luminance similarity. Our results showed a convincing replication at the aggregate and individual level. However, at the individual level, all observers showed grouping by proximity whereas some observers did not show grouping by luminance similarity. In response, we ran a second experiment with enlarged luminance differences to reinforce the strength of grouping by luminance similarity and balance the strength of the two grouping cues. Interestingly, in this second experiment, additivity was not observed but instead a significant interaction was obtained. This disparity suggests that the additivity or interaction between two grouping cues in a visual stimulus is not a general rule of perceptual grouping but a consequence of relative grouping strength.

Temporal synchrony is widely recognized as one of the key factors facilitating the emergence of crossmodal correspondences and affecting their crossmodal effects. However, several issues regarding the definition of temporal synchrony and the mechanisms underlying its crossmodal effects remain open, depending on the specific experimental/perceptual context/stimuli used, as well as the influence of crossmodal congruency and structural (including isomorphic) crossmodal correspondences. In this review, we take a closer look at the literature that has been published in this area over recent decades in order to critically evaluate what is currently known concerning the crossmodal effects that are mediated by temporal synchrony. We focus especially on mid-level audiovisual crossmodal correspondences, defined as those that involve multi-element, or dynamic, auditory and visual stimuli. We examine the different experimental methodologies used and their limitations as well as the theoretical frameworks that have been proposed to account for the viewer’s impression of (and the meaning/affect that is associated with) such experimental audiovisual displays, including those that are based on the ‘Congruency-Associationist Model’, Gestalt perceptual grouping, as well as the phenomenon of multisensory emergence. Finally, we outline several directions for future research on temporal synchrony in the context of audiovisual crossmodal correspondences.

Perceptual grouping, a fundamental mechanism in our visual system, significantly influences our interpretation of and interaction with the surrounding world. This study explores the impact of the proximity principle from the perspective of the Two Visual Systems (TVS) model. The TVS model argues that the visual system comprises two distinct streams: the ventral stream, which forms the neural basis for “vision-for-perception,” and the dorsal stream, which underlies “vision-for-action.” We designed a perceptual grouping task using dot lattices as well as a line-orientation discrimination task. Data were collected using vocal and mouse methods for the vision-for-perception mode, and joystick and pen-paper methods for the vision-for-action mode. Each method, except for vocal, included separate blocks for right and left hands. The proximity data were fitted using exponential and power models. Linear mixed-effects models were used for the statistical analyses. The results revealed similar line-orientation discrimination accuracy across all conditions. The exponential model emerged as the best fit, demonstrating adherence to the Pure Distance Law in both perceptual modes. Sensitivity to the proximity principle was higher in the vision-for-action mode compared to the vision-for-perception. In terms of orientation biases, a strong preference for vertical orientation was observed in the vision-for-perception mode, whereas a noticeable preference toward either of the oblique orientations was detected in the vision-for-action mode. Analysis of free-drawn lines demonstrated an affordance bias in the vision-for-action mode. This suggests a remarkable tendency to perceive organizations within specific orientations that offer more affordances due to the interaction between the body postures and tools.

Grouping by proximity is a fundamental principle of human vision where elements close to each other are perceived as a group. This study examined the hysteresis effect in proximity-based grouping of dots in rectangular lattices in the presence of orientation biases. To induce perceptual switching, interdot distances in a specific direction were gradually increased or decreased on a trial-by-trial basis during ascending and descending sequences. To address orientation biases, stimuli were presented along two axes, each with two orientations. This design allowed investigation of perceptual switching between vertical and horizontal grouping in the cardinal axis and between 45° and 135° grouping in the oblique axis. Data from 34 participants were analyzed by fitting psychometric functions and the Lotka-Volterra-Haken (LVH) model—a dynamical model of neural population competition—with statistical analysis using linear mixed-effects models. The results revealed a strong preference for the vertical orientation in the cardinal axis and a slight bias toward 135° in the oblique axis. A significant hysteresis effect was found in both axes, with ascending transition points consistently exceeded descending points. Interestingly, this effect remained unaffected by stimulus axis or orientation, indicating robustness against orientation biases. A significant positive correlation in hysteresis across axes suggests it may represent a personal perceptual characteristic. The LVH model’s numerical simulation effectively captured the dynamic behavior of competing responses and their bifurcation during perceptual switching. The model demonstrated acceptable accuracy in estimating transition points and simulating individual responses. Moreover, its parameters reflected the observed data patterns and provided a mechanistic account of perceptual switching in proximity-based grouping.

When responding to the identity of a visual target, nearby stimuli ( flankers ) that are associated with the same response as the target cause faster and more accurate responding than flankers that are associated with different responses. Because this flanker-congruence effect (FCE) decreases with increasing target-flanker separation, it was thought to reflect limited precision of spatial selection mechanisms. Later studies, however, showed that FCEs are larger when the target and flankers are the same color compared to when they are different colors. This led to the group selection hypothesis , which states that flankers are perceptually grouped with the target and are obligatorily selected along with it, regardless of spatial separation. An alternative hypothesis, the image segmentation hypothesis , states that feature differences facilitate the segmentation of visual information into relevant and irrelevant parts, thereby mitigating the limitations of spatial precision of selection mechanisms. We test between these hypotheses using a design in which targets and flankers are grouped or not grouped, while holding feature differences in the stimulus constant. Contrary to earlier results, we found that same-colored flankers do not yield larger FCEs than different-colored flankers when feature differences are held constant. We conclude that similarity effects on the FCE reflect differential support for image segmentation, on which selection depends, rather than the obligatory selection of perceptually grouped flankers and targets.

Holistic processing, demonstrated by a failure of selective attention to individual parts within stimuli, is often considered a relatively unique feature of the processing of faces and objects of expertise. However, face-like holistic processing has been recently demonstrated for novel line stimuli with salient Gestalt perceptual grouping cues. Further, disrupting such cues within face stimuli disrupts holistic face perception. There is evidence that holistic processing of these gestalt stimuli and faces does not overlap mechanistically in the same way as does the processing of faces and objects of expertise. However, the relationship between these different manifestations of holistic processing is unclear. We developed a task to probe whether a holistic processing-specific overlap occurs at an earlier, perceptual level between the mechanisms supporting processing of faces and strong gestalt stimuli. Faces and gestalt line stimuli were overlaid, and participants made part judgments about either the faces (Experiment 1 ) or line stimuli (Experiment 2 ) in a composite task indexing holistic perception. The data revealed evidence of reciprocal interference between holistic processing of line and face stimuli, with indices of holistic processing of face and line stimuli reduced when the overlaid stimuli were also processed holistically (e.g., intact line/face stimuli) compared with when the overlaid stimuli did not commandeer holistic processing resources (e.g., misaligned line/face stimuli). This pattern is consistent with a mechanistic overlap between the holistic perception of faces and gestalt stimuli. Our results support a dual—stimulus-based and experienced-based—pathway model of holistic processing, with face stimuli using both.