No disillusions in auditory extinction: perceiving a melody comprised of unperceived notes

Working Memory in Unilateral Spatial Neglect: Evidence for Impaired Binding of Object Identity and Object Location

Working memory (WM) is known to be impaired in patients with stroke experiencing unilateral spatial neglect (USN). Here, we examined in a systematic manner three WM components: memory of object identity, memory of object location, and binding between object identity and location. Moreover, we used two different retention intervals to isolate maintenance from other mnemonic and perceptual processes. Fourteen USN first-event stroke patients with right-hemisphere damage were tested in two different WM experiments using long and short retention intervals and an analog response scale. Patients exhibited more identification errors for items displayed on the contralesional side. Localization errors were also more prominent in the contralesional side, especially after a long retention interval. These localization errors were often a result of swap errors, that is, erroneous localizations of correctly identified contralesional objects in correctly memorized locations of ipsilesional objects. We conclude that a key WM deficit in USN is a lateralized impairment in binding between the identity of an object and its spatial tag.

The effect of illusionary perception on mismatch negativity (MMN): An electroencephalography study

Mismatch negativity (MMN) is a unique brain response elicited by any discernible change of features in a tone sequence. Although the occurrence of MMN is dependent upon the difference of a stimulus parameter, such as frequency or intensity, recent studies have suggested that MMN occurs as a result of a comparison between an internal representation created by perception and an incoming tone. The present study aimed to investigate MMN occurs based upon the physical properties of stimuli or as a result of the perception of the scale illusion. A scale illusion occurs during presentation of ascending and descending musical scales between C4 and C5. The tones of these scales are presented to the right and left ear alternately using a dichotic listening paradigm. Although the ascending/descending sequences are alternated between ears after each tone, we perceive the illusion of progressively ascending/descending tones as being separated by ear. The experiment was designed as an oddball task using the illusionary sequence and three different types of tone sequences as control conditions. Brain response to these sequences and infrequently presented deviants was measured using electroencephalography (EEG). All of the control sequences showed MMN in response to the deviant. However, the illusionary sequence did not result in a significant MMN. These results suggest that in the case of scale illusion, the occurrence of MMN is based upon the representation of tones created by perception, but not upon the physical properties of a tone sequence.

Hierarchy of prediction errors for auditory events in human temporal and frontal cortex

Predictive coding theories posit that neural networks learn statistical regularities in the environment for comparison with actual outcomes, signaling a prediction error (PE) when sensory deviation occurs. PE studies in audition have capitalized on low-frequency event-related potentials (LF-ERPs), such as the mismatch negativity. However, local cortical activity is well-indexed by higher-frequency bands [high-γ band (Hγ): 80-150 Hz]. We compared patterns of human Hγ and LF-ERPs in deviance detection using electrocorticographic recordings from subdural electrodes over frontal and temporal cortices. Patients listened to trains of task-irrelevant tones in two conditions differing in the predictability of a deviation from repetitive background stimuli (fully predictable vs. unpredictable deviants). We found deviance-related responses in both frequency bands over lateral temporal and inferior frontal cortex, with an earlier latency for Hγ than for LF-ERPs. Critically, frontal Hγ activity but not LF-ERPs discriminated between fully predictable and unpredictable changes, with frontal cortex sensitive to unpredictable events. The results highlight the role of frontal cortex and Hγ activity in deviance detection and PE generation.

Neural representation of scale illusion: magnetoencephalographic study on the auditory illusion induced by distinctive tone sequences in the two ears

The auditory illusory perception “scale illusion” occurs when a tone of ascending scale is presented in one ear, a tone of descending scale is presented simultaneously in the other ear, and vice versa. Most listeners hear illusory percepts of smooth pitch contours of the higher half of the scale in the right ear and the lower half in the left ear. Little is known about neural processes underlying the scale illusion. In this magnetoencephalographic study, we recorded steady-state responses to amplitude-modulated short tones having illusion-inducing pitch sequences, where the sound level of the modulated tones was manipulated to decrease monotonically with increase in pitch. The steady-state responses were decomposed into right- and left-sound components by means of separate modulation frequencies. It was found that the time course of the magnitude of response components of illusion-perceiving listeners was significantly correlated with smooth pitch contour of illusory percepts and that the time course of response components of stimulus-perceiving listeners was significantly correlated with discontinuous pitch contour of stimulus percepts in addition to the contour of illusory percepts. The results suggest that the percept of illusory pitch sequence was represented in the neural activity in or near the primary auditory cortex, i.e., the site of generation of auditory steady-state response, and that perception of scale illusion is maintained by automatic low-level processing.