raster = readGDAL("filename.TIFF")
summary(raster)
Object of class SpatialGridDataFrame
Coordinates:
   min max
x -180 180
y  -90  90
Is projected: FALSE
proj4string :
[+proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0]
Grid attributes:
  cellcentre.offset cellsize cells.dim
x            -179.5        1       360
y             -89.5        1       180
Data attributes:
     band1
 Min.   :  1.0
 1st Qu.:255.0
 Median :255.0
 Mean   :226.9
 3rd Qu.:255.0
 Max.   :255.0
 NA's   :245

head(data[7:8]) #Xp = longitude, Yp = latitude
              Xp        Yp
    7  -50.41777   1.33138
    8  -59.25075 -19.16780
    9  -67.25043 -27.83412
    10 -54.91759 -15.00130
    12 -67.58375 -28.00078
    13 -65.08385 -34.33386

sp <- SpatialPoints(data[7:8])
summary(sp)
Object of class SpatialPoints
Coordinates:
         min       max
Xp -76.08341 -35.25171
Yp -38.66702   1.33138
Is projected: NA
proj4string : [NA]
Number of points: 184

data$ndvi<-extract(raster, sp)
    Error in .subset(x, j) : invalid subscript type 'S4'

simr <- raster(ncol=36, nrow=18)
simr[] <- 1:ncell(simr)
simndvi<-extract(raster, sp)
head(simndvi)
[1] 301 373 408 373 408 444