  During solar flares, spectral lines formed in the photosphere have been shown
to exhibit changes to their profiles despite the challenges of energy transfer
to these depths. Recent work has shown that deep-forming spectral lines are
subject to significant contributions from regions above the photosphere
throughout the flaring period, resulting in a composite emergent intensity
profile from multiple layers of the atmosphere. We employ
radiative-hydrodynamic and radiative transfer calculations to simulate the
response of the solar/stellar atmosphere to electron beam heating and
synthesize spectral lines of Fe I to investigate the line-of-sight velocity
fields information available from Doppler shifts of the emergent intensity
profile. By utilizing the contribution function to deconstruct the line profile
shape into its constituent sources, we show that variations in the line
profiles are primarily caused by changes in the chromosphere. Up-flows in this
region were found to create blueshifts or "false" redshifts in the line core
dependent on the relative contribution of the chromosphere compared to the
photosphere. In extreme solar and stellar flare scenarios featuring explosive
chromospheric condensations, red-shifted transient components can dominate the
temporal evolution of the profile shape, requiring a tertiary component
consideration to fully characterize. We conclude that deep-forming lines
require a multi-component understanding and treatment, with different regions
of the spectral line being useful for probing individual regions of the
atmosphere's velocity flows.
