Open image in new window Fig. 2 Transverse images of a predominantly cystic left lobe nodule obtained without (left) and with (right) spatial and frequency compounding software.
Spatial compounding refers to composite images created by insonations from transmitted pulses at multiple different angles to the probe surface (Fig. 1) whilst frequency compounding generates images based on a range of frequencies across the probe bandwidth [4].
In cases of 0.5 median activity labels (i.e. the compounds was attributed the two possible labels with the same frequency), compounds were removed from the dataset by applying the "Row Filter" node.
c) Wavelength diversity, usually called frequency compounding.
For opaque compounds only, there was a larger MMN for high frequency than low frequency compounds.
Following the P3a, there was an increase in negativity around 400 ms, which was larger over frontal locations for transparent compared to opaque compounds, for low- compared to high-frequency compounds, and for pseudo-compounds compared to high frequency compounds.
Follow-up ANOVAs for each location separately indicated that high frequency compounds were associated with a significantly larger MMN response than low frequency compounds at central locations [ F 1, 17) = 6.066, p = .025].
The lack of frequency effects for transparent compounds is clear evidence against a purely lexical account of transparent compound processing (which would predict a lexical MMN: high frequency > low frequency compounds > pseudo-compounds).
There was no statistical difference between pseudo-compounds and low frequency compounds and effects at central and parietal locations were not significant.
The larger N400 for low frequency compared to high frequency compounds and for pseudo-compounds compared to transparent high frequency compounds correspond well to previously-observed frequency effects (Friedrich, Eulitz, & Lahiri, 2006; Van Petten & Kutas, 1990) and are well-explained in terms of more difficult integration during combinatorial processing of the constituents.
