Forensic nurse, AZ
09-20-06
ISU Study Finds Morphing Eyewitness Composites Better at Catching Criminals
AMES, Iowa -- In the latest high-profile investigation, an eyewitness composite
sketch of the woman suspected of stealing a 10-day-old infant and slashing the
mother's throat in Missouri was used. But prior research has found that facial
composites of criminal suspects built by individual eyewitness accounts often
produce poor likenesses of the actual perpetrators. Now, a new study by Iowa
State University professor of psychology Gary Wells and one of his PhD
students reports that the morphing together of composites made by four
individuals produces an image that better resembles a target face than an
individual composite, as long as the morphed composites don't become too
numerous.
"The problem with composites is that frankly, they don't look much like the
person," said Wells. "It's a difficult task for someone to come up with a composite
because we don't perceive faces piecemeal -- we don't store them in memory as
individual facial features, such as the nose, the eyes, or the mouth. Rather, the
facial processing is holistic. So in asking someone to come up with a composite,
we're asking people to do something that is totally unnatural."
Lisa Hasel, an ISU doctoral student in psychology, joined with Wells to author a
research paper titled, "Catching the Bad Guy: Morphing Composite Faces
Helps," which has been accepted for publication in the journal Law and Human
Behavior. The study was awarded a national prize by the Association for
Psychological Science.
The researchers selected 16 target faces from a large database of facial
photographs. Each was of 19- to 23-year-olds that fell into four different
categories: four Asian females with long black hair, four Caucasian females with
short brown hair, four Caucasian males with short brown hair, and four
Caucasian males with medium-length black hair.
Sixteen IowaState students participated in the composite generation phase of the
study, with 72 more participating in an initial attractiveness evaluation phase, and
another 60 in the similarity evaluation and second attractiveness evaluation
phase.
In the composite generation phase, participants were asked to look at one of four
different target faces in a specific category for one minute. After each face was
removed, they were asked to create four composites apiece using the facial
composite software called FACES. After building each composite, the creator
rated their own compositions for how similar they thought their composite was to
the face they had viewed. The four composites for each face were then morphed
together by an independent experimenter -- resulting in 64 individual composites
and 16 morphed composites.
Participants in the next phase rated the attractiveness of every face image,
comparing the overall attractiveness of the three face image categories -- photos
of target faces, composites, and morphs. The morphed composites were found to
be the most attractive of the three.
The final group also rated the attractiveness of the face images, as well as the
similarity of the individual composites and morphs to both the target and nontarget faces. Upon completing their ratings, they were asked to select from a face
array, which included the target face, which face looked the most similar to the
individual composites or morphs. The morphs produced a higher targetpreference rate (47.7 percent) than did individual composites (35.2 percent).
"Does morphing four composites into one represent a specific person better than
individual composites? The bottom line is that the answer is 'yes,'" said Wells.
But Wells also reported the following two side-effects associated with that
conclusion:
1. The morphed image was found to be more "attractive" than the individual
target faces.
"So if the perpetrator is an unattractive person, the morphed image may not work
as well because the resulting face may be too attractive," said Wells.
2. The morphed image better resembles the intended target face, but also better
resembles other faces who are not the intended target. "If you morph a number
of these composites together, you ultimately create a closer image to the
prototypical face," Wells said. "So if you put 10 composites together from
different people of the same types of face -- for example, white males -- they
would produce a morphed image that would look like the average white male. We
just went up to four in this study, and it does produce a better likeness of the
intended face, although it also does start resembling other faces in that general
category," he said. "It ultimately would produce more leads, but also a greater
chance of including the perpetrator of the crime."
According to Wells, this is the first real improvement to the tool of eyewitness
composites in a criminal investigation.
Source: Iowa State University