But what about now?

那現在呢？

You might remember more or less that I have pale skin and dark hair.

應該可以大概記得我的皮膚白晢和一頭深色的頭髮。

But what If I asked you to describe my nose?

但要你形容我的鼻子呢？

Would you say it was flat?

你會形容是扁的？

Long?

高的？

Pointy?

尖的？

And what about my eyes?

那我的眼睛呢？

Round?

圓圓的？

Almond shaped?

杏眼？

Wide set?

寬的？

Deep-set?

眼窩深？

Close together?

還是眼距近？

Difficult to be specific isn't it?

難以具體形容，對吧？

And that gives you some indication of the kinds of problems that detectives face when they're trying to recreate images of suspects.

這樣大概可以知道，警探需要面對需要重新描繪嫌疑犯的圖像時的問題會是什麼。

The idea behind police sketches is simple.

警方畫出素描背後的目的很簡單。

An eyewitness sees a crime and works with the police to create an image of the criminal.

目擊者目睹一宗罪案的發生經過，其後與警方合作畫出罪犯的圖像。

But how accurate are these kinds of sketches?

這些素描圖像的準確性有多高呢？

Do they really help catch criminals?

真的有助緝拿罪犯？

Experiments by forensic psychologists in the U.K. found that faces were identified correctly by police sketches in just 8 percent of cases.

根據英國的法證心理學家的實驗數據顯示，透過警方的素描圖像能成功認出罪犯的機率只有 8%。

There have been some cases where police sketches have worked well, such as the Oklahoma Bomber, Timothy McVeigh, and the sketch of serial killer Ted Bundy, which prompted people who knew Bundy to call the authorities.

警方的素描圖像在某些案件中還是起很大的作用，像是奧克拉荷馬市爆炸案中的主謀蒂莫西．麥克維以及連環殺手泰德．邦迪的素描圖像讓認識他的人聯絡有關當局。

But more often than not, the similarities are not that close and a police sketch ends up being mostly a guesstimate.

但往往圖像和本人並沒有很相似，警方的素描圖像都只能依推測作描繪。

And one reason it's so difficult to get them right is because our brains aren't wired to process each individual feature on a face.

難以準確描繪出的原因是因為我們的大腦是沒有辦法記得臉上的每一個特徵。

When the mind remembers a face it doesn't look at the face and break it up into databases of noses and eyes and ears and then try to reconstruct them, which is how the early systems work.

當我們的大腦記住一張臉的時候，並不是看著一張臉就可以把他們各自分拆至把眼、耳和鼻子的數據庫中，然後再把它們重新組合，而這是舊有的運作系統。

Instead, when we look at faces, we remember the whole face.

反而是看著一張臉的時候，我們記得的是整張臉。

So our mind is storing the face holistically.

就是說我們的大腦是記住整張臉。

When it comes to police sketches, the process of reconstructing a face from memory, detail by detail, is the opposite of how we naturally recall faces.

而警方的素描圖像需要透過記憶把人臉重現描述，要鉅細無遺地描繪是與我們一般記住人臉過程是相反的。

In the 60s and 70s, systems such as Identikit and Photofit tried to fix this problem with large databases of interchangeable features.

六、七十年代，開始透過艾登蒂基特容貌拼圖 (Identikit) 和 拼湊人像 (Photofit) 等系統的可互換面貌的大型數據庫以解決這方面的問題。

By the 80s, computerized systems such as E-FIT meant they could be a bit more customised, but the witness still had to scroll through lists of individual features, so any face constructed was limited by those options.

至八十年代，如 E-FIT 這類的電腦化系統的出現，可讓素描畫像更客制化，但是目擊者仍必須滾動瀏覽各個臉部特徵列表，因此任何組成的臉孔都受到這些選項限制。

And these aren't the only hurdles.

難題不僅只有這樣。

Not only do we find it difficult to identify individual features, we also struggle to describe them.

不僅是難以辨認每個臉部特徵，甚至更難以形容。

So when you see the face of a perpetrator, if you're unlucky enough to be a witness to a crime, you see the face, so it's visual.

當你看到行兇者的臉時，如此不幸地成為罪案的目擊者，你看到對方的臉，這是視覺性的。

But when the police officer asks you to describe it you have to give a verbal response and our brains aren't very good at swapping between modalities, swapping from the visual to the verbal.

但當警察要求你形容，你需要作用口頭上的回應。而我們大腦並不擅於形式上互換，從視覺轉換成語言。

And then there's the issue of time.

還有一個時間上的問題…

The problem is, is that witnesses are normally interviewed a couple of days or a week after a crime.

問題是目擊者通常都是在罪案發生後的幾天或一星期後才會做筆錄。

And when this happens, witnesses struggle to remember what the face looks like and they struggle to remember the parts of the face.

在做筆錄的時候，目擊者難以記起嫌疑犯的面貌，甚至無法記起臉上部位的特徵。

And what we know is, for unfamiliar faces, our memory tends to be particularly good for the hair and the outer part of the face.

據我們所知，對於不熟識的臉孔，我們較能記住髮型和臉型輪廓。

And yet when you become familiar with the face, it's the central internal features that you tend to rely on in order to be able to recognize somebody's faces.

當對那張臉孔變得熟悉時，為了能辨認某人的臉孔，臉部中間的特徵才是你會記得的部分。

So a witness will tend to construct the outer part of the face well, but somebody who's trying to recognize the face will be looking at the central part of the face.

意思是目擊者對於描繪臉部外圍的特徵會較好，但想要辨識出臉孔的則需要臉部中間的特徵。

And so there's a kind of a mismatch in what's accurate in the face.

因此會出現與臉部上準確的特徵錯配的情況。

And that's what has led to EvoFIT, a composite facial system that Charlie Frowd helped to develop.

於是就發展了 EvoFIT，一個由 Charlie Frowd 協助研發的人臉組合系統。

It presents randomly generated faces that users are able to tweak, adjusting them by variables such as pleasantness, attractiveness or honesty.

系統會隨機產生多個人臉，使用者可根據和藹、吸引力或誠實程度等可變的臉部特徵再作調整。

We built a system that shows witnesses screens of faces and they're asked to select faces that look like the person that they've seen.

我們建立的這個系統可以向目擊者顯示很多張不同的臉，他們要根據自己看到的選出最相似的。

Those choices are then combined together and another screen is produced.

之後會把選好的部分組合起來，產出另外一個影像。

In some of the experiments what we've been doing is showing witnesses faces where the outer part is de-emphasized or blurred to help a witness focus on the central part of the face.

我們有一些實驗是向目擊者展示已把臉形外圍部分淡化或模糊的圖像，以幫助目擊者將注意力集中於臉部中央的部分。

And that's actually quite effective to help people construct the central part of the face more accurate and so produce a more identifiable composite.

結果顯示是有效幫助他們更準確地組合臉部中間的特徵，以描繪出辨識度較高的複合圖像。

We've shown in the laboratory identification can be about 75 percent correct.

我們在實驗室中的結果顯示的識別率大約是 75％。

I mean so, performance that really is quite good and actually valuable for police and for policing.

可見這方法的表現蠻好，對於警方辦案和巡查時非常有用。

EvoFIT helped catch a serial rapist in Manchester who was recognised by a facial composite on Crimewatch and turned in to the police by his own brother.

透過 EvoFIT 系統幫助緝拿了一名曼徹斯特的連環強姦犯，該名罪犯的臉部組合圖像於於 Crimewatch (英國電視節目) 被辨認出，並由他的兄弟向警察求助。

Very often perhaps the facial composite images aren't that accurate, but nonetheless, they can be an invaluable prompt to somebody who maybe looks at it and thinks, "Is that someone I know?"

很多時候臉部組合的圖像並不夠準確，然而對於可能看過圖中人的民眾來說，這可能是一個寶貴的提示「是我認識的人嗎？」

And that can be all that's needed to push them over the line and call the police and say, "I think it's this person."

這就已足以推使他們去想並報警說「我想就是他了！」