4.3. Brain-Behavior Relationships
Contrary to our expectations, at the inter-individual level the amount
of change of the target-elicited N250 from the first to the second
experiment half did not correlate with memory performance. Since these
correlations were essentially zero, we suspect that this null result is
not due to a lack of power or a low signal-to-noise ratio, as indicated
by the high split-half reliabilities of the target-elicited N250 and the
good to excellent reliability of the face memory test results. Rather it
seems that the robust increase in N250 amplitude across the experiment,
although possibly reflecting increasing familiarity with the designated
target face, is not related to individual differences in face
recognition. One conceivable reason is the ease of recognizing the
target face, leading to a ceiling effect.
The relationship of the across-session changes of the N250 to non-target
faces and memory performance was significant only between N250 to
low-distinctive faces and performance in the easy but not in the
difficult memory task. Wilhelm et al. (2010) and Hildebrandt et al.
(2010) have demonstrated in large samples that face cognition in easy
and difficult tasks must be distinguished, similar to the need for such
a distinction when measuring general cognitive abilities. Therefore, it
is an interesting finding that also the brain-behavior relationship
seems to be specific for the kind of memory task – the association with
the easy task was double in effect size than with the hard task. The
simplest explanation for the unverifiable association between the
across-session change of the N250 and performance in the difficult
memory test is the lower reliability of the accuracy than of the
recognition speed test. However, since our sample size was only modest
and memory task performance was measured on the manifest level, it
remains important to replicate these findings with a larger sample and
to investigate a set of indicators for testing these associations at the
latent level.
Interestingly, the brain-behavior relations of the easy task performance
were found for across-session N250-changes in ERPs to low-distinctive
rather than to high-distinctive faces. Intuitively, one might expect a
stronger relationship between the neural signal of building-up a memory
trace of high-distinctive faces and face recognition performance than
for the harder to process low-distinctive faces. However, the stronger
relationship found for across-session increases in low-distinctive
face-elicited N250 may become plausible when considering that the ERP
task required the discrimination of the low-distinctive target face from
the likewise low-distinctive non-target faces. Individuals with better
face recognition ability may have solved this task by a faster build-up
of a representation of these non-target faces, as manifested in a larger
N250 amplitude increase across the session. In contrast, memory
representations for high-distinctive non-target faces may not have been
necessary to make the distinction from the non-distinctive target face.
To the best of our knowledge this is the first study that shows a
brain-behavior relationship between the N250 to faces and face memory.
Hence, the present results extend previous findings from the N250r
(Herzmann et al., 2010; Kaltwasser et al. 2014) to a condition where the
N250 amplitude evolves across multiple presentations. Since the
difference of the N250 across experimental halves can also be considered
a kind of repetition effect, it would be of interest, whether the
difference between experimental halves in the N250 is related to the
N250r. This would be of particular interest, considering the close
conceptual relations of these components.