About the NEWBI Experiment

In developing these tutorials, we wanted an experiment that used at least one brain area that shows robust activation and one brain area that is less well explored. As such, we chose to study faces and hands. Images of faces reliably activate a right-hemisphere lateralized network of regions1,2 that includes the well-studied Fusiform Face Area (FFA) 3 Images of hands activate a scarcely explored region of the lateral occipitotemporal cortex (LOTChand) 4.

We also wanted a main experiment that would be amenable to various designs (e.g., block vs. event-related designs), analyses (e.g., univariate subtractions vs. multivariate pattern analysis), and strategies (e.g., region-of-interest vs. voxelwise approaches).

We decided to test whether activation levels (and perhaps activation patterns and functional connectivity) differ between faces and hands that are directed toward the observer vs. away. Behavioral evidence shows that participants respond faster to a target when primed by a face looking toward vs. away from the target 5 .

Given brain-activation differences between faces that differ in gaze direction (direct vs. sideways; left vs. right) 6 , we expected that we could replicate these differences and explore a more novel question of whether activation differences existed for images of pointing hands (direct vs. sideways; left vs. right), which have also shown behavioural differences 7 .

The main experiment was a 2x3 factorial design that crossed stimulus category (faces vs. hands) with stimulus orientation (left, centre, right), as shown in example stimuli in Figure 1.

Figure 1: Example stimuli for main experiment

Figure 1: Example stimuli for main experiment

Figure 2: Example stimuli for localizer runs

Figure 2: Example stimuli for localizer runs

In addition to the main experiment, we also collected localizer data as well as data from variations on the localizer design. Localizer runs, consisting of runs with face, hand, body, scrambled images (Figure 2), will provide the opportunity to conduct region-of-interest analyses using independent data. Variant runs, described at the end of this page, will be used in lectures and upcoming tutorials to explore the effect different (suboptimal) design parameters have on brain activation measures.

Participants

Data from a group (14 participants) will be utilized for the core analyses in the exercises. Data were collected from three additional participants but were discarded because one showed excessive/abrupt motion and two had only 5 main experiment scans available (fewer than the 6 used for most analysis).

Participant age, sex, and handedness have not yet been compiled. All participants had normal or corrected-to-normal vision and were financially compensated. Informed consent was obtained prior to scanning. All experimental procedures were approved by the University of Western Ontario’s Health Sciences Research Ethics Board.

Experimental Design and Timing

Localizers

Video 1: Localizer stimuli excerpt

Localizer stimuli enabled identification of brain regions selective to three categories of visual stimuli: faces, hands, and bodies8. These categories could be compared against a fourth stimulus type - scrambled versions of the same images - to identify brain regions that respond to coherent visual stimuli.

Participants were instructed to maintain their gaze on a central fixation point, which was also presented on a blank screen during baseline periods. Participants monitored the stream of visual stimuli for repetitions (a one-back task) to maintain attention. Video 1 shows a short excerpt of the visual stimuli presented to participants in the localizer run.

 

Images were presented to subjects according to a conventional block design, with a block duration of 16 s (Figure 3). Each block consisted of 16 stimuli, each presented for 0.8 s with a 0.2-s intertrial interval. Four cycles of four blocks (faces, hands, bodies, scrambled images) were presented in each run. Baseline blocks (also 16 s) occurred at the beginning and end of each run and between cycles. The total run duration was 336 s (21 blocks x 16 s/block). The order of blocks within cycles was balanced such that for a run, each category was presented once in each of the first, second, third and fourth part of the cycle. Two runs with two different orders were collected. The order for Localizer 1 is visualized in Figure 4.

Figure 4: Localizer 1 block order

Figure 4: Localizer 1 block order

 
Figure 3: Stimuli for face, hand, body and scrambled blocks

Figure 3: Stimuli for face, hand, body and scrambled blocks

Main experiment

As shown in Figure 1, stimuli in the main experiment formed a 2 x 3 factorial design with image category (faces/hands) and orientation (left/centre/right). Orientation indicated direction of eye gaze and direction of pointed index finger, for faces and hands, respectively. A static fixation point and a one-back task were also used in the main experiment.

Images were presented in a rapid event-related design with a total run duration of 280 s. Baseline blocks (16 s) occurred at the beginning and end of each run. The remaining 248 s were divided into 62 trials (4 s/trial). According to 10 different, shuffled run orders, a balanced subset of the visual stimuli was presented over 51 trials (including 3 one-back stimuli). The remaining 11 trials were randomly interspersed non-consecutive null stimuli. Six runs with six different orders were collected. For each subject, a different combination of run orders (210 possible) was used. An example of one experimental run order is visualized by Figure 4. Examples of stimuli used in experimental runs are shown in Video 2.

Video 2: Main experiment stimuli excerpt

 
Figure 5: Example of main experiment stimuli order

Figure 5: Example of main experiment stimuli order

 

MRI Acquisition

All scans were collected using a Siemens Magnetom Prisma 3-Tesla MRI scanner at the Centre for Functional and Metabolic Mapping at the Robarts Research Institute of Western University. Functional scans utilized 2.5-mm isotropic resolution with a matrix size of 84×84 over 52 slices, repetition time (TR) = 1000ms, multi-band gradient-echo echoplanar pulse sequence. Anatomical scans were collected using T1-weighted 3D MPRAGE sequence with a matrix size of 248×256 over 176 1-mm slices.

Data Preprocessing

Data were preprocessed in Brain Voyager 20.6-22 software. Standard preprocessing steps for the primary pipeline consisted of functional-anatomical alignment, three-dimensional motion correction, temporal high-pass filtering, transformation into 2-mm isotropic resolution, and warping into stereotaxic space using the MNI-152 template.

References

  1. Haxby, J. V., Hoffman, E. A. & Gobbini, M. I. The distributed human neural system for face perception. Trends Cogn. Sci. 4, 223–233 (2000).

  2. Kanwisher, N. & Yovel, G. The fusiform face area: A cortical region specialized for the perception of faces. Philos. Trans. R. Soc. B Biol. Sci. 361, 2109–2128 (2006).

  3. Kanwisher, N., McDermott, J. & Chun, M. M. The fusiform face area: a module in human extrastriate cortex specialized for face perception. J. Neurosci. 17, 4302–11 (1997).

  4. Bracci, S., Ietswaart, M., Peelen, M. V & Cavina-Pratesi, C. Dissociable neural responses to hands and non-hand body parts in human left extrastriate visual cortex. J. Neurophysiol. 103, 3389–97 (2010).

  5. Friesen, C. K. & Kingstone, A. The eyes have it! reflexive orienting is triggered by nonpredictive gaze - download. Psychon. Bull. Rev. 5, 490–495 (1998).

  6. George, N., Driver, J. & Dolan, R. J. Seen gaze-direction modulates fusiform activity and its coupling with other brain areas during face processing. Neuroimage 13, 1102–1112 (2001).

  7. Nishimura, A. & Michimata, C. Pointing Hand Stimuli Induce Spatial Compatibility Effects and Effector Priming. Front. Psychol. 4, 1–8 (2013).

  8. Downing, P. E. et al. A cortical area selective for visual processing of the human body. Science 293, 2470–3 (2001).