Eye Movements in Reading: Recent Developments

When we read, our eyes do not move smoothly across the page of text as our phenomenological im pressions imply. Rather, we make a series of eye movements (referred to as saccades) separated by periods of time when the eyes are relatively still (fixations). Eye movements are nec essary during reading because of acuity limitations in the visual sys tem. A line of text extending around the point of fixation can be divided into three regions: foveal, parafoveal, and peripheral. The foveal region is the center of vision (extending 1? of visual angle to the left and right of fixation), where acu ity is sharpest, enabling us to resolve the letters in the text easily. In the parafoveal region (extending out to 5? of visual angle on either side of fixation) and the peripheral region (everything on the line beyond the parafoveal region), acuity drops off markedly so that our ability to iden tify letters is not very good even in the near parafovea. The purpose of eye movements in reading is there fore to place the foveal region on that part of the text we wish to pro cess next. The basic facts about eye move ments during reading have been known for some time. The typical saccade is about eight to nine letter spaces; this value is not affected by the size of the print as long as it is not too small or too large. The ap propriate metric to use when dis cussing eye movements during read ing is therefore letter spaces, and not visual angle; generally, three to four letter spaces is equivalent to 1? of visual angle. Because of the high ve locity of the saccade, no useful in formation is acquired while the eyes are moving; readers acquire infor mation from the text during fixa tions. The average fixation duration is about a quarter of a second (250 ms). The other primary characteristic of eye movements during reading is that about 10% to 15% of the time, we move our eyes back in the text (regressions) to look at material that we have already read. It is also important to note that as text difficulty increases, fixation du ration increases, saccade length de creases, and regression frequency increases. More important, the val ues just presented are averages, and there is considerable variability in the measures, both between and within readers. Thus, although the average fixation duration for a given reader might be 250 ms, for others it could be on the order of 200, 235, 280, or 300 ms. The average sac cade length and regression fre quency also vary across readers. As far as within-subject variability is concerned, although a reader's av erage fixation duration might be 250 ms, the range could be from under 100 ms to over 500 ms within a pas sage of text. Likewise, although the average saccade length for a given reader might be 8 letter spaces, the range could be from 1 letter to over 15 (though such long saccades typi cally follow regressions). A great deal of recent research has docu mented that the variability in these measures is related to the ease or dif ficulty associated with processing the text. Since the mid-1970s, there has been a resurgence of interest in us ing eye movement data to study the reading process.1 Researchers have typically been interested in eye movements during reading for two reasons: (1) to describe the charac teristics of the eye movements per se and (2) to use eye movement data to infer something about perceptual and cognitive processes during read ing. Because most of the work in my laboratory has focused on the latter issue, the major focus of this article is on processing during reading.