Does visual working memory represent a fixed number of objects, or is capacity reduced as object complexity increases? We measured accuracy in detecting changes between sample and test displays and found that capacity estimates dropped as complexity increased. However, these apparent capacity reductions were strongly correlated with increases in sample-test similarity (r= .97), raising the possibility that change detection was limited by errors in comparing the sample and test, rather than by the number of items that were maintained in working memory. Accordingly, when sample-test similarity was low, capacity estimates for even the most complex objects were equivalent to the estimate for the simplest objects (r= .88), suggesting that visual working memory represents a fixed number of items regardless of complexity. Finally, a correlational analysis suggested a two-factor model of working memory ability, in which the number and resolution of representations in working memory correspond to distinct dimensions of memory ability.

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The functional organization of human auditory cortex has not yet been characterized beyond a rudimentary level of detail. Here, we use functional MRI to measure the microstructure of orthogonal tonotopic and periodotopic gradients forming complete auditory field maps (AFMs) in human core and belt auditory cortex. These AFMs show clear homologies to subfields of auditory cortex identified in nonhuman primates and in human cytoarchitectural studies. In addition, we present measurements of the macrostructural organization of these AFMs into "clover leaf" clusters, consistent with the macrostructural organization seen across human visual cortex. As auditory cortex is at the interface between peripheral hearing and central processes, improved understanding of the organization of this system could open the door to a better understanding of the transformation from auditory spectrotemporal signals to higher-order information such as speech categories.tonotopy | periodotopy | cochleotopy | temporal receptive field | traveling wave H umans have evolved a highly sophisticated auditory system for the transduction and analysis of acoustic information, such as the spectral content of sounds and the temporal modulation of sound energy. The basilar membrane of the cochlea is organized tonotopically to represent the spectral content of sounds from high to low frequencies. This tonotopic (or cochleotopic) organization is preserved as auditory information is processed and passed on from the cochlea to the superior olive, the inferior colliculus, the medial geniculate nucleus, and into primary auditory cortex. Such cortical preservation of the peripheral sensory topography creates a common topographic sensory matrix in hierarchically organized sensory systems, important for consistent sensory computations. The current state of knowledge of the functional organization of human auditory cortex indicates the existence of multiple cortical subfields organized tonotopically. However, the number of these human cortical subfields, their boundaries, and their orientations relative to anatomical landmarks remain equivocal, due in part to an inability to measure cortical representations of a second acoustic dimension orthogonal to tonotopy to accurately delineate them.This ambiguity of human auditory subfield definitions contrasts dramatically with the current understanding of the functional organization of human visual cortex, in which detailed maps of the organization of the retina, called visual field maps (VFMs), have been well characterized (1-9). In vision, there are two orthogonal dimensions of visual space, eccentricity and polar angle, which together allow for the mapping of cortical representations to unique locations in visual space and the complete delineation of the boundaries of individual visual field maps. In audition, there has been only one dimension of sensory topography clearly mapped in cortex, which makes it impossible to use sensory topography to accurately differentiate specific human cortical auditory field maps (AFM...

Crowding refers to the phenomenon in which nearby distractors impede target processing. This effect is reduced as target-distractor distance increases, and it is eliminated entirely at a distance that is labeled the critical spacing point. Attention, distractor preview, and popout are each known to facilitate processing in crowded displays. Eight experiments examined whether this is accomplished via a reduction in critical spacing. Attention was manipulated via spatial cueing, whereby a peripheral cue elicited a stimulus-driven shift of attention. Distractor preview was examined by manipulating whether the crowding distractors were presented prior to or simultaneous with the target. Popout was examined by manipulating whether there was a salient color difference between the target and distractors. As demonstrated in previous studies, we found robust benefits of spatial cueing, preview, and popout in crowded displays. However, although spatial cueing led to robust improvements in target discrimination, there was no reduction in critical spacing for attended stimuli. By contrast, both preview and popout caused large reductions in critical spacing. These disparate results indicate that attention improves target discrimination in crowded displays in a qualitatively different manner than do the other factors.