Kernel Flow: a high channel count scalable time-domain functional near-infrared spectroscopy system.

Significance: Time-domain functional near-infrared spectroscopy (TD-fNIRS) has been considered as the gold standard of noninvasive optical brain imaging devices. However, due to the high cost, complexity, and large form factor, it has not been as widely adopted as continuous wave NIRS systems.

Aim: Kernel Flow is a TD-fNIRS system that has been designed to break through these limitations by maintaining the performance of a research grade TD-fNIRS system while integrating all of the components into a small modular device.

Evaluating perceptual integration: uniting response-time- and accuracy-based methodologies.

This investigation brings together a response-time system identification methodology (e.g., Townsend & Wenger Psychonomic Bulletin & Review 11, 391-418, 2004a) and an accuracy methodology, intended to assess models of integration across stimulus dimensions (features, modalities, etc.

Prioritized Detection of Personally Familiar Faces.

We investigated whether personally familiar faces are preferentially processed in conditions of reduced attentional resources and in the absence of conscious awareness. In the first experiment, we used Rapid Serial Visual Presentation (RSVP) to test the susceptibility of familiar faces and faces of strangers to the attentional blink. In the second experiment, we used continuous flash interocular suppression to render stimuli invisible and measured face detection time for personally familiar faces as compared to faces of strangers.

Processing of invisible social cues.

Successful interactions between people are dependent on rapid recognition of social cues. We investigated whether head direction--a powerful social signal--is processed in the absence of conscious awareness. We used continuous flash interocular suppression to render stimuli invisible and compared the reaction time for face detection when faces were turned towards the viewer and turned slightly away.

Attentive and pre-attentive processes in change detection and identification.

In studies of change blindness, observers often have the phenomenological impression that the blindness is overcome all at once, so that change detection, localization and identification apparently occur together. Three experiments are described that explore dissociations between these processes using a discrete trial procedure in which 2 visual frames are presented sequentially with no intervening inter-frame-interval. The results reveal that change detection and localization are essentially perfect under these conditions regardless of the number of elements in the display, which is consistent with the idea that change detection and localization are mediated by pre-attentive parallel processes.

On the minimization of task switch costs following long-term training.

Flexible, context-dependent linkages between stimulus and response are fundamental to adaptive behavior. In the present article, we evaluate the limits of this flexibility by exploring the asymptotic efficiency of people's ability to switch between two different sensorimotor mappings. Two stimulus-response (S-R) mappings were learned, either both on the same hand (unimanual condition) or one mapping per hand (intermanual condition).

Inhibitory processes mediate saccadic target selection.

Observers (N = 3, all males, M age = 30.7 yr.) were presented pairs of visual targets and instructed to fixate one as quickly as possible.

Failures to see: attentive blank stares revealed by change blindness.

Change blindness illustrates a remarkable limitation in visual processing by demonstrating that substantial changes in a visual scene can go undetected. Because these changes can ultimately be detected using top-down driven search processes, many theories assign a central role to spatial attention in overcoming change blindness. Surprisingly, it has been reported that change blindness can occur during blink-contingent changes even when observers fixate the changing location [O'Regan, J.

Multimodal access to verbal name codes.

Congruent information conveyed over different sensory modalities often facilitates a variety of cognitive processes, including speech perception (Sumby & Pollack, 1954). Since auditory processing is substantially faster than visual processing, auditory-visual integration can occur over a surprisingly wide temporal window (Stein, 1998). We investigated the processing architecture mediating the integration of acoustic digit names with corresponding symbolic visual forms.

Smooth pursuit of nonvisual motion.

Unlike saccades, smooth pursuit eye movements (SPEMs) are not under voluntary control and their initiation generally requires a moving visual target. However, there are various reports of limited smooth pursuit of the motion of a subject's own finger in total darkness (pursuit based on proprioceptive feedback) and to the combination of proprioception and tactile motion as an unseen finger was moved voluntarily over a smooth surface. In contrast, SPEMs to auditory motion are not distinguishable from pursuit of imagined motion.

Directional uncertainty in visually guided pointing.

Studies of the relationship between stimulus-response uncertainty and reaction times indicate three qualitatively different functions: Hick's law, simple-choice step function, or flat curve (no effect at all). The extent of stimulus-response S-R) compatibility appears to interact with the effects of uncertainty on response times. One possible hypothesis regarding these various S-R uncertainty functions is that uncertainty will have an effect whenever the stimuli and their associated responses are not within the same egocentric spatial coordinates.

Effects of directional uncertainty on visually-guided joystick pointing.

Reaction times generally follow the predictions of Hick's law as stimulus-response uncertainty increases, although notable exceptions include the oculomotor system. Saccadic and smooth pursuit eye movement reaction times are independent of stimulus-response uncertainty. Previous research showed that joystick pointing to targets, a motor analog of saccadic eye movements, is only modestly affected by increased stimulus-response uncertainty; however, a no-uncertainty condition (simple reaction time to 1 possible target) was not included.

Effects of stimulus-response uncertainty on saccades to near-threshold targets.

Kveraga et al. (2002, Exp Brain Res 146(3):307-14) reported that saccade latencies are immune to the effects of stimulus-response uncertainty and constitute one of the few response systems that violate Hick's law. Similar effects have been reported for keypresses triggered by vibrations of the fingertips, but robust uncertainty effects were subsequently revealed using weak, low-frequency vibrations (Ten Hoopen et al.

Ocular tracking as a measure of auditory motion perception.

Motion is a potent sub-modality of vision. Motion cues alone can be used to segment images into figure and ground and break camouflage. Specific patterns of motion support vivid percepts of form, guide locomotion by specifying directional heading and the passage of objects, and in case of an impending collision, the time to impact.

Smooth pursuit under stimulus-response uncertainty.

Simple reaction times (RTs) are typically faster than choice reaction times and increase with uncertainty according to Hick's law. Here we show that smooth pursuit eye movement RTs show no effect of SR uncertainty while joystick tracking shows a step change between SRT and CRT, but no significant increases beyond two choices. The results suggest there is a benefit to pre-programming joystick tracking but not for smooth pursuit eye movements (SPEMs).

Saccades operate in violation of Hick's law.

Hick's law states that response times (RTs) increase in proportion to the logarithm of the number of potential stimulus-response (S-R) alternatives. We hypothesized that time-consuming processes associated with response selection contribute significantly to this effect. We also hypothesized that the latency of saccades might not conform to Hick's law since visually guided saccades can be automatically selected using topographically organized pathways that convert spatially coded visual activity into spatially coded motor commands.