The phrase "a visual observation of" is correct and usable in written English.
It can be used when describing the act of observing something visually, often in contexts like research, art, or analysis.
Example: "The study involved a visual observation of the subjects' behavior in their natural habitat."
Alternatives: "a visual inspection of" or "a visual assessment of".
A visual observation of the red-oil samples before and during the trial was performed.
Fig. 3 A Visual observation of ammonia production by strain PF1 (a) and control (b) test.
The selection of points was firstly guided by a visual observation of paint color, texture and morphology.
The tasks represented neural activities arising from a visual observation of a motor action related to hand movements of the subjects.
A visual observation of the flow from the outside of the column does not yield the desired information, especially for large-scale pilot-plant reactors.
From a visual observation of Fig. 4a, b, there is a very positive correlation between predicted porosity from the two neural networks scheme and observed porosity, respectively, as shown in the alignment results (dots) obtained by the two neural networks around the lines (fit line and ideal line).
Unlike previous systems, the structure of the device allowed a constant visual observation of cell growth over the whole membrane surface.
Finally, by a simple visual observation of the colony advance edge of both the wild-type and Δ recA strains, we can rule out any effect of RecA on the production of slime because the slime that normally surrounds the colony periphery was, apparently, similar in both cases (data not shown).
Devolatilization of a single fuel particle and the related flame combustion were studied in a two-dimensional fluidized bed with a quartz wall, allowing visual observation of the conversion process.
A positive test result was based upon visual observation of a grey- white immunoprecipitate in the agarose gel.
As a consequence, diagnosis using visual observation of the foot without further laboratory tests is commonly used by researchers and clinicians once D. nodosus is endemic in a flock.
