Auditory short-term memory behaves like visual short-term memory

Spectro-temporal modulation transfer function of single voxels in the human auditory cortex measured with high-resolution fMRI

Are visual and auditory stimuli processed by similar mechanisms in the human cerebral cortex? Images can be thought of as light energy modulations over two spatial dimensions, and low-level visual areas analyze images by decomposition into spatial frequencies. Similarly, sounds are energy modulations over time and frequency, and they can be identified and discriminated by the content of such modulations. An obvious question is therefore whether human auditory areas, in direct analogy to visual areas, represent the spectro-temporal modulation content of acoustic stimuli. To answer this question, we measured spectro-temporal modulation transfer functions of single voxels in the human auditory cortex with functional magnetic resonance imaging. We presented dynamic ripples, complex broadband stimuli with a drifting sinusoidal spectral envelope. Dynamic ripples are the auditory equivalent of the gratings often used in studies of the visual system. We demonstrate selective tuning to combined spectro-temporal modulations in the primary and secondary auditory cortex. We describe several types of modulation transfer functions, extracting different spectro-temporal features, with a high degree of interaction between spectral and temporal parameters. The overall low-pass modulation rate preference of the cortex matches the modulation content of natural sounds. These results demonstrate that combined spectro-temporal modulations are represented in the human auditory cortex, and suggest that complex signals are decomposed and processed according to their modulation content, the same transformation used by the visual system.

Intracranial electroencephalography reveals two distinct similarity effects during item recognition

Behavioral studies of visual recognition memory indicate that old/new decisions reflect both the similarity of the probe to the studied items (probe-item similarity) and the similarities among the studied items themselves (list homogeneity). Recording intracranial electroencephalography from 1,155 electrodes across 15 patients, we examined the oscillatory correlates of probe-item similarity and homogeneity effects in short-term recognition memory for synthetic faces. Frontal areas show increases in low-frequency oscillations with both probe-item and item-item similarity, whereas temporal lobe areas show distinct oscillatory correlates for probe-item similarity and homogeneity in the gamma band. We discuss these frontal low-frequency effects and the dissociation in the temporal lobe in terms of recent computational models of visual recognition memory.

The temporal interaction of modality specific and process specific neural networks supporting simple working memory tasks

Several theories of brain function emphasize distinctions between sensory and cognitive systems. We hypothesized, instead, that sensory and cognitive systems interact to instantiate the task at the neural level. We tested whether input modality interacts with working memory operations in that, despite similar cognitive demands, differences in the anatomical locations or temporal dynamics of activations following auditory or visual input would not be limited to the sensory cortices. We recorded event-related brain potentials (ERPs) while participants performed simple short-term memory tasks involving visually or auditorily presented bandpass-filtered noise stimuli. Our analyses suggested that working memory operations in each modality had a very similar spatial distribution of current sources outside the sensory cortices, but differed in terms of time course. Specifically, information for visual processing was updated and held online in a manner that was different from auditory processing, which was done mostly after the offset of the final stimulus. Our results suggest that the neural networks that support working memory operations have different temporal dynamics for auditory and visual material, even when the stimuli are matched in term of discriminability, and are designed to undergo very similar transformations when they are encoded and retrieved from memory.

A cognitive approach to the development of early language

A controversial issue in the field of language development is whether language emergence and growth is dependent solely on processes specifically tied to language or could also depend on basic cognitive processes that affect all aspects of cognitive competence (domain-general processes). The present article examines this issue using a large battery of infant information-processing measures of memory, representational competence, processing speed, and attention, many of which have been shown to predict general cognition in a cohort of full-terms and preterms. Results showed that various aspects of infant memory and representational competence (a) related to language at both 12 and 36 months, (b) predicted similarly for the two groups, and (c) predicted 36-month language, independently of birth status, 12-month language, and the 12-month Bayley Mental Development Index. Additionally, the results established predictive validity for the MacArthur 12-month language measure. These findings support a domain-general view of language.

Trial-to-trial carryover in auditory short-term memory

Using a short-term recognition memory task, the authors evaluated the carryover across trials of 2 types of auditory information: the characteristics of individual study sounds (item information) and the relationships between the study sounds (study set homogeneity). On each trial, subjects heard 2 successive broadband study sounds and then decided whether a subsequently presented probe sound had been in the study set. On some trials, the similarity of the probe item to stimuli presented on the preceding trial was manipulated. This item information interfered with recognition, and false alarms increased from 0.4% to 4.4%. Moreover, the interference was tuned so that only stimuli that were very similar to each other interfered. On other trials, the relationship among stimuli was manipulated to alter the criterion subjects used in making recognition judgments. The effect of this manipulation was confined to the trial on which the criterion change was generated and did not affect the subsequent trial. These results demonstrate the existence of a sharply tuned carryover of auditory item information but no carryover of the effects of study set homogeneity.

Modulation of ventral prefrontal cortex functional connections reflects the interplay of cognitive processes and stimulus characteristics

Emerging ideas of brain function emphasize the context-dependency of regional contributions to cognitive operations, where the function of a particular region is constrained by its pattern of functional connectivity. We used functional magnetic resonance imaging to examine how modality of input (auditory or visual) affects prefrontal cortex (PFC) functional connectivity for simple working memory tasks. The hypothesis was that PFC would show contextually dependent changes in functional connectivity in relation to the modality of input despite similar cognitive demands. Participants were presented with auditory or visual bandpass-filtered noise stimuli, and performed 2 simple short-term memory tasks. Brain activation patterns independently mapped onto modality and task demands. Analysis of right ventral PFC functional connectivity, however, suggested these activity patterns interact. One functional connectivity pattern showed task differences independent of stimulus modality and involved ventromedial and dorsolateral prefrontal and occipitoparietal cortices. A second pattern showed task differences that varied with modality, engaging superior temporal and occipital association regions. Importantly, these association regions showed nonzero functional connectivity in all conditions, rather than showing a zero connectivity in one modality and nonzero in the other. These results underscore the interactive nature of brain processing, where modality-specific and process-specific networks interact for normal cognitive operations.

Characterizing the ERP Old-New effect in a short-term memory task

The early and late components of the event-related potential (ERP) Old-New effect are well characterized with respect to long-term memory, and have been associated with processes of familiarity and recollection, respectively. Now, using a short-term memory paradigm with verbal and nonverbal stimuli, we explored the way that these two components respond to variation in recency and stimulus type. We found that the amplitude of the early component (or frontal N400, FN400) showed Old-New effects only for verbal stimuli and increased with recency. In contrast, the later component (or late positive component, LPC) showed Old-New effects across a range of stimulus types and did not scale with recency. These results are consistent with the way that these same ERP components have been characterized in long-term memory, supporting the idea that some of the same processes underlie long- and short-term item recognition.

Recognition and position information in working memory for visual textures

In three experiments, we examined connections between item-recognition memory and memory for item-position information. With sequences of compound gratings as study and probe items, subjects made either item-position judgments (Experiments 1 and 2), by identifying the serial position of the study item that matched the probe, or recognition judgments (Experiment 3), by judging whether the probe had or had not been presented in the study series. Integrating a summed-similarity account of recognition into a signal detection framework shows that the variance of summed similarities on lure trials (probe not present in the study series) exceeds the variance on target trials (probe present in the study series). This prediction is borne out by the empirical zROC functions, all of which had slopes that were greater than 1. Additionally, about 25% of correct recognitions were accompanied by incorrect item position identification. Misidentifications of item position arose from two sources--structural similarity and positional similarity-which combined in an approximately additive fashion.

Auditory change detection: simple sounds are not memorized better than complex sounds

Previous research has shown that the detectability of a local change in a visual image is essentially independent of the complexity of the image when the interstimulus interval (ISI) is very short, but is limited by a low-capacity memory system when the ISI exceeds 100 ms. In the study reported here, listeners made same/different judgments on pairs of successive "chords" (sums of pure tones with random frequencies). The change to be detected was always a frequency shift in one of the tones, and which tone would change was unpredictable. Performance worsened as the number of tones increased, but this effect was not larger for 2-s ISIs than for 0-ms ISIs. Similar results were obtained when a chord was followed by a single tone that had to be judged as higher or lower than the closest component of the chord. Overall, our data suggest that change detection is based on different mechanisms in audition and vision.

Recognition memory for realistic synthetic faces

A series of experiments examined short-term recognition memory for trios of briefly presented, synthetic human faces derived from three real human faces. The stimuli were a graded series of faces, which differed by varying known amounts from the face of the average female. Faces based on each of the three real faces were transformed so as to lie along orthogonal axes in a 3-D face space. Experiment 1 showed that the synthetic faces' perceptual similarity structure strongly influenced recognition memory. Results were fit by a noisy exemplar model (NEMO) of perceptual recognition memory. The fits revealed thatrecognition memory was influenced both by the similarity of the probe to the series items and by the similarities among the series items themselves. Nonmetric multidimensional scaling (MDS) showed that the faces' perceptual representations largely preserved the 3-D space in which the face stimuli were arrayed. NEMO gave a better account of the results when similarity was defined as perceptual MDS similarity, rather than as the physical proximity of one face to another. Experiment 2 confirmed the importance of within-list homogeneity directly, without mediation of a model. We discuss the affinities and differences between visual memory for synthetic faces and memory for simpler stimuli.