Objects seen as scenes: neural circuitry for attending whole or parts

Depending on our goals, we pay attention to the global shape of an object or to the local shape of its parts, since it’s difficult to do both at once. This typically effortless process can be impaired in disease. However, it is not clear which cortical regions carry the information needed to constrain shape processing to a chosen global/local level. Here, novel stimuli were used to dissociate functional MRI responses to global and local shapes. This allowed identification of cortical regions containing information about level (independent from shape). Crucially, these regions overlapped part of the cortical network implicated in scene processing. As expected, shape information (independent of level) was mainly located in category-selective areas specialized for object- and face-processing. Regions with the same informational profile were strongly linked (as measured by functional connectivity), but were weak when the profiles diverged. Specifically, in the ventral-temporal-cortex (VTC) regions favoring level and shape were consistently separated by the mid-fusiform sulcus (MFS). These regions also had limited crosstalk despite their spatial proximity, thus defining two functional pathways within VTC. We hypothesize that object hierarchical level is processed by neural circuitry that also analyses spatial layout in scenes, contributing to the control of the spatial-scale used for shape recognition. Use of level information tolerant to shape changes could guide whole/part attentional selection but facilitate illusory shape/level conjunctions under impoverished vision.Significance statementOne daily engages hierarchically organized objects (e.g. face-eyes-eyelashes). Their perception is commonly studied with global shapes composed by of local shapes. Seeing shape at one level is easy, but difficult for both at once. How can the brain guide attention to one level? Here using novel stimuli that dissociate different levels over time and examining local patterns of brain-activity, we found that the level and shape of visual objects were represented into segregated sets of cortical regions, each connected into their own pathway. Level information was found in part of the cortical network known to process scenes. Coding of object-level independently from shape could participate in guiding sustained attention within objects, eliminating interference from irrelevant levels. It could also help produce “illusory conjunctions” (perceptual migration of a shape to the wrong level) when attention is limited.HighlightsModified Navon figures allow dissociation in time of fMRI responses for the global/local levels.Shape-invariant hierarchical level information was found in scenes selective areas, whereas level-invariant shape information was found in object- and faces- selective areas.Level and shape regions were divided by the mid-fusiform sulcus (MFS) in VTC cortex, and each type of region connected into its own pathway.Having separate level/shape pathways could facilitate selective-attention, but foster illusory conjunctions.

Conclusion

The Conclusion draws together the findings concerning music and speech that are explored in the book, and the insights derived from these findings. Much of the book is concerned with illusions. Some of the illusions reflect huge differences between people in how they perceive simple musical patterns. These differences suggest variations in brain organization and environmental exposure. Another way in which these illusions shed light on hearing involves illusory conjunctions. These lead to the conclusion that, normally, the process of analyzing sound includes the operation of specialized modules that each analyze a particular attribute, and that we combine the outputs of these modules to obtain an integrated percept. This process usually leads us to perceive sounds correctly, but it breaks down under certain circumstances, producing illusions. Further threads that run through the book involve relationships between music and speech; the importance of unconscious inference, or “top-down processing” on our perception of sound; and extremes of musical ability, which are shown to be the products of both innate and environmental factors. It is also shown that earworms and musical hallucinations highlight the vital role played by the inner workings of our musical minds in determining what we hear. The extraordinary phenomena explored in this book lead us to conclude that the hearing mechanism did not arise as a coherent, integrated whole, but rather developed as a set of different, though interconnected, mechanisms. From another perspective, they elucidate factors involved in listening to music in everyday life.

Crowding and binding: Not all feature-dimensions behave in the same way

Humans often fail to identify a target because of nearby flankers. The nature and stage(s) at which this 'crowding' occurs are unclear, and whether crowding operates via a common mechanism across visual dimensions is unknown. Using a dual estimation report, we quantitatively assessed the processing of each feature alone and in conjunction with another feature both within and between dimensions. Crowding emerged due to confusion between orientations or colors of target and flankers, but averaging of their spatial frequencies (SFs). Furthermore, crowding of orientation and color were independent, but crowding of orientation and SF were interdependent. This qualitative difference of crowding errors across dimensions revealed a tight link between crowding and 'illusory conjunctions' (mis-binding of feature dimensions). These results and a computational model suggest that crowding and illusory conjunction in the visual periphery are due to pooling across a joint coding of orientation and spatial frequencies but not of color.

Separability of Tones and Rhymes in Chinese Speech Perception: Evidence from Perceptual Migrations

This study used the perceptual-migration paradigm to explore whether Mandarin tones and syllable rhymes are processed separately during Mandarin speech perception. Following the logic of illusory conjunctions, we calculated the cross-ear migration of tones, rhymes, and their combination in Chinese and English listeners. For Chinese listeners, tones migrated more than rhymes. For English listeners, the opposite pattern was found. The results lend empirical support to autosegmental theory, which claims separability and mobility between tonal and segmental representations. They also provide evidence that such representations and their involvement in perception are deeply shaped by a listener’s linguistic experience.

What Can Illusory Conjunctions Reveal About Synaesthetic Bindings?

The visual system successfully binds the shapes and colours of objects; therefore, our visual experience regarding the objects around us is coherent. However, this binding process can break down when attention is diverted, producing illusory conjunctions (ICs); for example, when presented with a red 2 and a green 5, the observer may report a green 2 and a red 5. The strongest observation of binding in human cognition is found in synaesthesia. In grapheme–colour synaesthesia, linguistic stimuli (e.g., letters or numbers) are strongly associated with colours. It is debatable whether these highly stable bindings constitute a form of early binding that occurs outside the focus of attention. We examined for the first time the occurrence of ICs in grapheme–colour synaesthesia. Experiment 1 replicated our previous finding, showing the effects of numerical distance on ICs (Arend et al., Psychon. Bull. Rev. 2013, 20, 1181–1186). Participants viewed a display containing two centrally presented letters and two coloured numbers and were asked to report: (1) whether the letters were same/different, (2) the colour of the larger number, and (3) the level of confidence concerning the colour of the number. Experiment 2 used a modified version of this task. Synaesthetes () and controls () viewed number–colour pairs that were congruent or incongruent with that of the synaesthetic association. Grapheme–colour synaesthesia significantly affected ICs on incongruent but not on congruent trials. Our findings strongly support the notion that shape and colour are free-floating features in synaesthesia, similar to what is observed in normal cognition.